Stockholders' Equity - Summary of Stock Appreciation Rights Activity (Detail) (Stock Appreciation Rights [Member], USD $)	9 Months Ended
	Sep. 30, 2014
Stock Appreciation Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock appreciation rights, Outstanding at December 31, 2013	806,116
Number of stock appreciation rights, Granted
Number of stock appreciation rights, Exercised	(58,850)
Number of stock appreciation rights, Forfeited	(10,384)
Number of stock appreciation rights, Outstanding at September 30, 2014	736,882
Number of stock appreciation rights, Vested and exercisable at September 30, 2014	494,136
Weighted Average Exercise Price, Outstanding at December 31, 2013	$ 23.98
Weighted Average Exercise Price, Granted
Weighted Average Exercise Price, Exercised	$ 23.71
Weighted Average Exercise Price, Forfeited	$ 24.40
Weighted Average Exercise Price, Outstanding at September 30, 2014	$ 23.99
Weighted Average Exercise Price, Vested and exercisable at September 30, 2014	$ 24.01
Weighted Average Remaining Contractual Term (in years), Outstanding at September 30, 2014	7 years 11 days
Weighted Average Remaining Contractual Term (in years), Vested and exercisable at September 30, 2014	6 years 11 months 9 days
Aggregate Intrinsic Value, Outstanding at September 30, 2014	$ 55.2
Aggregate Intrinsic Value, Vested and exercisable at September 30, 2014	$ 37.0