Stockholders' Equity - Summary of Stock Appreciation Rights Activity (Detail) (Stock appreciation rights [Member], USD $)	6 Months Ended
	Jun. 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	(22,410)
Number of Rights, Forfeited
Number of Rights, Outstanding at June 30, 2013	861,190
Number of Rights, Vested and exercisable at June 30, 2013	294,790
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
Weighted Average Exercise Price, Outstanding at June 30, 2013	$ 23.93
Weighted Average Exercise Price, Vested and exercisable at June 30, 2013	$ 23.97
Weighted Average Remaining Contractual Term (in years), Outstanding at June 30, 2013	8 years 5 months 23 days
Weighted Average Remaining Contractual Term (in years), Vested and exercisable at June 30, 2013	8 years 5 months 19 days
Aggregate Intrinsic Value, Outstanding at June 30, 2013	$ 21.8
Aggregate Intrinsic Value, Vested and exercisable at June 30, 2013	$ 7.4