Debt - Additional Information (Detail) (Credit Agreement [Member], USD $) In Thousands, unless otherwise specified	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 21, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Credit Agreement [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 325,000
Additional revolving commitments or term loan commitments under the New Credit Agreement	125,000
Revolving credit facility, maturity date	Mar. 21, 2015
Borrowings under the New Credit Agreement		$ 60,000		$ 60,000
Effective interest rate on borrowings		4.10%	2.70%	3.40%	2.30%
Commitment fee under the New Credit Agreement				0.40%