Debt - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 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
Commencement date of senior notes payment	Mar. 15, 2013
Repurchase agreement maximum loan borrowing capacity	25,000
Expiration date of repurchase agreement	Jul. 30, 2014
Debt outstanding under repurchase agreement	0
Borrowing base	$ 0