Annual report pursuant to Section 13 and 15(d)

Acquisitions - Finite-Lived Intangible Assets Acquired (Details)

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Acquisitions - Finite-Lived Intangible Assets Acquired (Details) - USD ($)
$ in Thousands
 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Business Acquisition [Line Items]    
Amortization period 10 years 7 months 6 days  
Intangible assets, net $ 151,434 $ 86,178
Industrial Process Insulators, Inc.    
Business Acquisition [Line Items]    
Amortization period 7 years 2 months 12 days  
Gross carrying amount $ 8,589 8,589
Accumulated Amortization 3,311 2,069
Intangible assets, net 5,278 $ 6,520
Thermon Heating Systems Inc.    
Business Acquisition [Line Items]    
Gross Carrying Amount 78,996  
Accumulated Amortization 4,311  
Net Carrying Amount $ 74,685  
Products | Thermon Heating Systems Inc.    
Business Acquisition [Line Items]    
Amortization period 10 years  
Gross Carrying Amount $ 64,611  
Accumulated Amortization 2,692  
Net Carrying Amount 61,919  
Customer relationships | Industrial Process Insulators, Inc.    
Business Acquisition [Line Items]    
Amortization period   8 years
Gross carrying amount 5,962 $ 5,962
Accumulated Amortization 1,987 1,242
Intangible assets, net $ 3,975 $ 4,720
Customer relationships | Thermon Heating Systems Inc.    
Business Acquisition [Line Items]    
Amortization period 17 years  
Gross Carrying Amount $ 11,155  
Accumulated Amortization 273  
Net Carrying Amount $ 10,882  
Backlog | Thermon Heating Systems Inc.    
Business Acquisition [Line Items]    
Amortization period 1 year  
Gross Carrying Amount $ 3,230  
Accumulated Amortization 1,346  
Net Carrying Amount 1,884  
Trademarks | Industrial Process Insulators, Inc.    
Business Acquisition [Line Items]    
Amortization period   8 years
Gross carrying amount 1,820 $ 1,820
Accumulated Amortization 607 379
Intangible assets, net 1,213 $ 1,441
Other Intangible Assets | Industrial Process Insulators, Inc.    
Business Acquisition [Line Items]    
Amortization period   3 years
Gross carrying amount 807 $ 807
Accumulated Amortization 717 448
Intangible assets, net $ 90 $ 359