Debt - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
Debt Disclosure [Abstract]
Senior notes principal amount	$ 600,000
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
Repurchase agreement maximum loan borrowing capacity	25,000
Borrowing base	0
Debt outstanding under repurchase agreement	$ 0
Expiration date of repurchase agreement	Jul. 29, 2015