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Debt - Additional Information (Detail) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2016
Dec. 31, 2015
Revolving Credit Facility [Member]    
Debt Instrument [Line Items]    
Repurchase agreement maximum loan borrowing capacity $ 150,000,000  
Repurchase agreement current loan borrowing capacity $ 145,000,000  
Expiration date of repurchase agreement Jul. 27, 2016  
Debt outstanding under repurchase agreement $ 0  
Increase in commitment available under repurchase agreement 50,000,000  
Senior Notes due 2022 [Member]    
Debt Instrument [Line Items]    
Senior notes principal amount $ 600,000,000  
Senior notes effective interest rate 3.97%  
Senior notes maturity Sep. 15, 2022  
Senior notes interest rate 3.95%  
Frequency of senior notes payment semi-annually in arrears on March 15 and September 15  
Debt issuance cost $ 3,285,000 $ 3,413,000