Stockholders' Equity - Summary of Stock Appreciation Rights Activity (Detail) (Stock appreciation rights [Member], USD $)	3 Months Ended
	Mar. 31, 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	(9,508)
Number of Rights, Forfeited
Number of Rights, Outstanding at March 31, 2013	874,092
Number of Rights, Vested and exercisable at March 31, 2013	259,144
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 March 31, 2013	$ 23.92
Weighted Average Exercise Price, Vested and exercisable at March 31, 2013	$ 23.96
Weighted Average Remaining Contractual Term (in years), Outstanding at March 31, 2013	8 years 8 months 23 days
Weighted Average Remaining Contractual Term (in years), Vested and exercisable at March 31, 2013	8 years 8 months 19 days
Aggregate Intrinsic Value, Outstanding at March 31, 2013	$ 20.0
Aggregate Intrinsic Value, Vested and exercisable at March 31, 2013	$ 5.9