Annual report pursuant to Section 13 and 15(d)

Long-Term Debt (Details)

v3.19.2
Long-Term Debt (Details)
$ in Thousands
9 Months Ended 12 Months Ended
Dec. 31, 2020
Oct. 30, 2017
CAD ($)
Oct. 30, 2017
USD ($)
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2018
Mar. 31, 2019
USD ($)
Mar. 31, 2018
USD ($)
Mar. 31, 2017
USD ($)
Apr. 01, 2018
Debt Instrument [Line Items]                    
Less current portion             $ (2,500,000) $ (2,500,000)    
Long-term debt, noncurrent             197,729,000 214,533,000    
Debt issuance costs, net             6,271,000 7,967,000    
Repayments of Long-term Debt             40,323,000 116,000,000 $ 13,500,000  
Debt Instrument, Debt Covenant, Maximum Leverage Ratio to Secure Additional Borrowing   4.0 4.0              
Borrowings under revolving credit facility             $ 11,225,000 0    
Outstanding borrowings from revolving line of credit                    
Debt Instrument [Line Items]                    
Interest rate at period end (as a percent)             4.57%      
Capacity available under credit facility             $ 44,469,000      
Borrowings under revolving credit facility             11,225      
Outstanding principal amount of senior secured credit facility                    
Debt Instrument [Line Items]                    
Long-term debt             200,229,000 217,033,000    
Period One | Outstanding principal amount of senior secured credit facility                    
Debt Instrument [Line Items]                    
Repayments of Notes Payable             625,000      
Period Three | Outstanding principal amount of senior secured credit facility                    
Debt Instrument [Line Items]                    
Repayments of Notes Payable             16,000,000 25,000,000    
Outstanding borrowings from revolving line of credit                    
Debt Instrument [Line Items]                    
Borrowings under revolving credit facility             $ 11,225,000 $ 0    
Outstanding borrowings from revolving line of credit | Line of Credit                    
Debt Instrument [Line Items]                    
Debt instrument, face amount     $ 60,000,000              
Debt instrument term   5 years 5 years              
Maximum leverage ratio           5.5        
Repayments of Lines of Credit     $ 6,000,000              
Consideration transferred, liabilities incurred   $ 201,900                
Line of Credit Facility, Commitment Fee Percentage   0.50% 0.50%              
Debt Instrument, Debt Covenant, Coverage Ratio   1.25 1.25              
Variable Rate Senior Secured Term Loan B | Secured Debt                    
Debt Instrument [Line Items]                    
Debt instrument, face amount     $ 250,000,000              
Debt instrument term   7 years 7 years              
Debt Instrument, Variable Interest Rate Floor     1.00%              
Debt Instrument, Quarterly Amortization, Percent                   0.25%
Debt Instrument, Prepayment Premium   1.00% 1.00%              
Debt Instrument, Debt Covenant, Repayment requirement, Percentage of Excess Cash Flow             50.00%      
Debt Instrument, Debt Covenant, Reduced Repayment Requirement, Percentage of Excess Cash Flow             25.00%      
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      
Line of Credit Facility, Additional Borrowing Capacity     $ 30,000,000              
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 | Outstanding borrowings from revolving line of credit | Line of Credit                    
Debt Instrument [Line Items]                    
Maximum leverage ratio 3.75     4.5 5.0          
Subsidiary Equity | Variable Rate Senior Secured Term Loan B | Secured Debt                    
Debt Instrument [Line Items]                    
Guarantor Obligations, Liquidation Proceeds, Percentage   100.00% 100.00%              
Stock of First Tier Material Foreign Subsidiaries, Domestic Borrower, and Domestic Subsidiary | Variable Rate Senior Secured Term Loan B | Secured Debt                    
Debt Instrument [Line Items]                    
Guarantor Obligations, Liquidation Proceeds, Percentage   65.00% 65.00%              
Base Rate | Outstanding borrowings from revolving line of credit | Line of Credit                    
Debt Instrument [Line Items]                    
Debt Instrument, Basis Spread on Variable Rate   2.25% 2.25%              
Base Rate | Variable Rate Senior Secured Term Loan B | Secured Debt                    
Debt Instrument [Line Items]                    
Debt Instrument, Basis Spread on Variable Rate   2.75% 2.75%              
London Interbank Offered Rate (LIBOR) | Outstanding borrowings from revolving line of credit | Line of Credit                    
Debt Instrument [Line Items]                    
Debt Instrument, Basis Spread on Variable Rate   3.25% 3.25%              
London Interbank Offered Rate (LIBOR) | Variable Rate Senior Secured Term Loan B | Secured Debt                    
Debt Instrument [Line Items]                    
Debt Instrument, Basis Spread on Variable Rate   3.75% 3.75%              
Canadian Base Rate | Outstanding borrowings from revolving line of credit | Line of Credit                    
Debt Instrument [Line Items]                    
Debt Instrument, Basis Spread on Variable Rate   2.25% 2.25%              
CDOR | Outstanding borrowings from revolving line of credit | Line of Credit                    
Debt Instrument [Line Items]                    
Debt Instrument, Basis Spread on Variable Rate   3.25% 3.25%