Stockholders' Equity - Summary of Stock Appreciation Rights Activity (Detail) (Stock appreciation rights [Member], USD $)	9 Months Ended
	Sep. 30, 2013
Stock appreciation rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Rights, Outstanding at December 31, 2012	883,600
Number of Rights, Granted
Number of Rights, Exercised	(34,046)
Number of Rights, Forfeited	(18,338)
Number of Rights, Outstanding at September 30, 2013	831,216
Number of Rights, Vested and exercisable at September 30, 2013	345,044
Weighted Average Exercise Price, Outstanding at December 31, 2012	$ 23.91
Weighted Average Exercise Price, Granted
Weighted Average Exercise Price, Exercised	$ 23.20
Weighted Average Exercise Price, Forfeited	$ 23.20
Weighted Average Exercise Price, Outstanding at September 30, 2013	$ 23.95
Weighted Average Exercise Price, Vested and exercisable at September 30, 2013	$ 23.99
Weighted Average Remaining Contractual Term (in years), Outstanding at September 30, 2013	8 years 2 months 9 days
Weighted Average Remaining Contractual Term (in years), Vested and exercisable at September 30, 2013	8 years 1 month 28 days
Aggregate Intrinsic Value, Outstanding at September 30, 2013	$ 29.9
Aggregate Intrinsic Value, Vested and exercisable at September 30, 2013	$ 12.4