Quarterly report pursuant to Section 13 or 15(d)

Long-Term Debt (Details)

v3.10.0.1
Long-Term Debt (Details)
$ in Thousands
6 Months Ended 9 Months Ended 12 Months Ended
Dec. 31, 2020
Oct. 30, 2017
CAD ($)
Oct. 30, 2017
USD ($)
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2018
USD ($)
Mar. 31, 2019
Apr. 01, 2018
Mar. 31, 2018
USD ($)
Debt Instrument [Line Items]                      
Less current portion       $ (2,500,000)       $ (2,500,000)     $ (2,500,000)
Long-term debt, net of current maturities and deferred debt issuance costs and debt discounts of $7,263 and $7,967 as of September 30, 2018 and March 31, 2018, respectively       210,987,000       210,987,000     214,533,000
Debt issuance costs       7,263,000       7,263,000     7,967,000
Debt issuance costs, net       7,263,000       7,263,000     7,967,000
Repayments of long-term debt       17,790,000 $ 14,125,000            
Maximum leverage ratio to secure additional borrowing   4.0 4.0                
Outstanding borrowings       8,497,000       8,497,000     0
Loans Payable                      
Debt Instrument [Line Items]                      
Debt Instrument, face amount                     5,905,000
Revolving credit facility                      
Debt Instrument [Line Items]                      
Outstanding borrowings       $ 8,497,000       $ 8,497,000      
Interest rate at period end (as a percent)       4.74%       4.74%      
Capacity available under credit facility       $ 46,587,000       $ 46,587,000      
Through March 31, 2019 | Loans Payable                      
Debt Instrument [Line Items]                      
Repayments of notes payable       1,000              
Revolving credit facility                      
Debt Instrument [Line Items]                      
Outstanding borrowings       8,497,000       $ 8,497,000     0
Revolving credit facility | Line of Credit                      
Debt Instrument [Line Items]                      
Debt Instrument, face amount     $ 60,000,000                
Repayments of lines of credit     $ 6,000,000                
Business Combination, Consideration Transferred, Liabilities Incurred   $ 201,900                  
Line of credit facility, commitment fee percentage   0.50% 0.50%                
Maximum leverage ratio               5.5      
Debt covenant, coverage ratio   1.25 1.25                
Revolving credit facility | Base Rate | Line of Credit                      
Debt Instrument [Line Items]                      
Basis spread on variable rate   2.25% 2.25%                
Revolving credit facility | London Interbank Offered Rate (LIBOR) | Line of Credit                      
Debt Instrument [Line Items]                      
Basis spread on variable rate   3.25% 3.25%                
Revolving credit facility | Canadian Base Rate [Member] | Line of Credit                      
Debt Instrument [Line Items]                      
Basis spread on variable rate   2.25% 2.25%                
Revolving credit facility | CDOR | Line of Credit                      
Debt Instrument [Line Items]                      
Basis spread on variable rate   3.25% 3.25%                
Variable Rate Term Loan due October 2024 | Loans Payable                      
Debt Instrument [Line Items]                      
Variable Rate Term Loans       213,487,000       $ 213,487,000     $ 217,033,000
Debt issuance costs, net       9,089,000       9,089,000      
Variable Rate Term Loan due April 2019 | Loans Payable                      
Debt Instrument [Line Items]                      
Debt issuance costs, net       $ 524,000       $ 524,000      
Variable Rate Senior Secured Term Loan B | Secured Debt                      
Debt Instrument [Line Items]                      
Debt Instrument, face amount     $ 250,000,000                
Variable interest rate floor     1.00%                
Quarterly amortization of debt, percent                   0.25%  
Repayment requirement, percentage of excess cash flow       50.00%              
Reduced repayment requirement, percentage of excess cash flow       25.00%              
Additional borrowing capacity     $ 30,000,000                
Variable Rate Senior Secured Term Loan B | Secured Debt | Subsidiary Stock                      
Debt Instrument [Line Items]                      
Guarantor obligations, percentage   100.00% 100.00%                
Variable Rate Senior Secured Term Loan B | Secured Debt | Stock of First Tier Material Foreign Subsidiaries, US Borrower, and US Subsidiary                      
Debt Instrument [Line Items]                      
Guarantor obligations, percentage   65.00% 65.00%                
Variable Rate Senior Secured Term Loan B | Base Rate | Secured Debt                      
Debt Instrument [Line Items]                      
Basis spread on variable rate   2.75% 2.75%                
Variable Rate Senior Secured Term Loan B | London Interbank Offered Rate (LIBOR) | Secured Debt                      
Debt Instrument [Line Items]                      
Basis spread on variable rate   3.75% 3.75%                
Term Loan A due April 2019                      
Debt Instrument [Line Items]                      
Repayments of long-term debt     $ 70,875,000                
Thermon Heating Systems Inc.                      
Debt Instrument [Line Items]                      
Debt proceeds used as consideration for business acquisition     $ 164,900,000                
Scenario, Forecast [Member] | Revolving credit facility | Line of Credit                      
Debt Instrument [Line Items]                      
Maximum leverage ratio 3.75         4.5 5.0        
Scenario, Forecast [Member] | Variable Rate Senior Secured Term Loan B | Secured Debt                      
Debt Instrument [Line Items]                      
Debt Instrument, Debt Covenant, Maximum Leverage Ratio Requirement For Reduced Repayment                 4.0    
Debt Instrument, Debt Covenant, Minimum Leverage Ratio Requirement For Reduced Repayment                 3.5    
Debt Instrument, Debt Covenant, Minimum Repayment Requirement, Percentage of Excess Cash Flow                 0.00%    
Debt Instrument, Debt Covenant, Maximum Leverage Ratio Requirement For Minimum Repayment                 3.5