Annual report pursuant to Section 13 and 15(d)

Goodwill and Other Intangible Assets - Narrative (Details)

v2.4.1.9
Goodwill and Other Intangible Assets - Narrative (Details) (USD $)
 12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2013
Mar. 02, 2015
Acquired Finite-Lived Intangible Assets [Line Items]        
Amortization of intangible assets $ 10,775,000us-gaap_AmortizationOfIntangibleAssets $ 11,090,000us-gaap_AmortizationOfIntangibleAssets $ 11,211,000us-gaap_AmortizationOfIntangibleAssets  
CHS Transactions [Member]        
Acquired Finite-Lived Intangible Assets [Line Items]        
Weighted average useful life of intangible assets 10 years      
CHS Transactions [Member] | Developed Technology Rights [Member]        
Acquired Finite-Lived Intangible Assets [Line Items]        
Estimated lives of intangible assets 20 years      
CHS Transactions [Member] | Backlog [Member]        
Acquired Finite-Lived Intangible Assets [Line Items]        
Estimated lives of intangible assets 4 months      
CHS Transactions [Member] | Customer Relationships [Member]        
Acquired Finite-Lived Intangible Assets [Line Items]        
Estimated lives of intangible assets 10 years      
CHS Transactions [Member] | Other [Member]        
Acquired Finite-Lived Intangible Assets [Line Items]        
Estimated lives of intangible assets 6 years      
Unitemp        
Acquired Finite-Lived Intangible Assets [Line Items]        
Amount of purchase price held in escrow       $ 351thr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedHeldinEscrow
/ us-gaap_BusinessAcquisitionAxis
= thr_UnitempMember
Weighted average useful life of intangible assets 6 years 8 months 10 days      
Unitemp | Developed Technology Rights [Member]        
Acquired Finite-Lived Intangible Assets [Line Items]        
Estimated lives of intangible assets 3 years      
Unitemp | Customer Relationships [Member]        
Acquired Finite-Lived Intangible Assets [Line Items]        
Estimated lives of intangible assets 5 years