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Debt - Additional Information (Detail) - USD ($)
12 Months Ended
Jan. 18, 2016
Dec. 31, 2015
Dec. 31, 2014
Revolving Credit Facility [Member]      
Debt Instrument [Line Items]      
Repurchase agreement maximum loan borrowing capacity   $ 25,000,000  
Expiration date of repurchase agreement   Jul. 27, 2016  
Repurchase facility maximum pricing rate   2.70%  
Debt outstanding under repurchase agreement   $ 0 $ 0
Borrowing base   $ 0  
Revolving Credit Facility [Member] | Subsequent Event [Member]      
Debt Instrument [Line Items]      
Repurchase agreement maximum loan borrowing capacity $ 150,000,000    
Increase in commitment available under repurchase agreement $ 50,000,000    
Senior Notes due 2022 [Member]      
Debt Instrument [Line Items]      
Debt issuance date   Sep. 10, 2012  
Senior notes principal amount   $ 600,000,000  
Senior notes maturity   Sep. 15, 2022  
Senior notes effective interest rate   3.97%  
Senior notes proceeds   $ 593,900,000  
Senior notes interest rate   3.95%  
Frequency of senior notes payment   semi-annually in arrears on March 15 and September 15