Stockholders' Equity - Summary of Stock Appreciation Rights Activity (Detail) - Equity Incentive Plan [Member] - Stock appreciation rights [Member] $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock appreciation rights, Outstanding at December 31, 2014	1,376,456
Number of stock appreciation rights, Granted	0
Number of stock appreciation rights, Exercised	(55,048)
Number of stock appreciation rights, Forfeited	(17,156)
Number of stock appreciation rights, Outstanding at September 30, 2015	1,304,252
Number of stock appreciation rights, Vested and exercisable at September 30, 2015	1,213,404
Weighted Average Exercise Price, Outstanding at December 31, 2014 | $ / shares	$ 12.03
Weighted Average Exercise Price, Granted | $ / shares	0
Weighted Average Exercise Price, Exercised | $ / shares	11.60
Weighted Average Exercise Price, Forfeited | $ / shares	11.60
Weighted Average Exercise Price, Outstanding at September 30, 2015 | $ / shares	12.05
Weighted Average Exercise Price, Vested and exercisable at September 30, 2015 | $ / shares	$ 12.05
Weighted Average Remaining Contractual Term (in years), Outstanding at September 30, 2015	6 years 2 months 9 days
Weighted Average Remaining Contractual Term (in years), Vested and exercisable at September 30, 2015	6 years 2 months 5 days
Aggregate Intrinsic Value, Outstanding at September 30, 2015 | $	$ 39.7
Aggregate Intrinsic Value, Vested and exercisable at September 30, 2015 | $	$ 36.9