Stock-based Compensation - Summary of Stock Appreciation Rights (Detail) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($) $ / shares shares
Time-Based Stock Appreciation Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Outstanding, Beginning Balance	3,853,367
Number of Shares, Granted	483,000
Number of Shares, Exercised	(128,050)
Number of Shares, Forfeited or expired	(75,100)
Number of Shares, Outstanding, Ending Balance	4,133,217
Number of Shares, Exercisable	3,300,317
Number of Shares, Vested and expected to vest	4,133,217
Weighted-Average Exercise Price, Outstanding, Beginning Balance | $ / shares	$ 4.53
Weighted-Average Exercise Price, Granted | $ / shares	6.07
Weighted-Average Exercise Price, Exercised | $ / shares	4.05
Weighted-Average Exercise Price, Forfeited or expired | $ / shares	6.50
Weighted-Average Exercise Price, Outstanding, Ending Balance | $ / shares	4.69
Weighted-Average Exercise Price, Exercisable | $ / shares	4.25
Weighted-Average Exercise Price, Vested and expected to vest | $ / shares	$ 4.69
Weighted-Average Remaining Contractual Term, Outstanding	5 years 10 months 28 days
Weighted-Average Remaining Contractual Term, Exercisable	5 years 4 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	5 years 10 months 28 days
Aggregate Intrinsic Value, Outstanding, Ending balance | $	$ 4,753
Aggregate Intrinsic Value, Exercisable | $	4,934
Aggregate Intrinsic Value, Vested and expected to vest | $	$ 4,753
Performance-Based Stock Appreciation Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Outstanding, Beginning Balance	786,034
Number of Shares, Granted	8,000
Number of Shares, Exercised	(11,200)
Number of Shares, Forfeited or expired	(160)
Number of Shares, Outstanding, Ending Balance	782,674
Number of Shares, Exercisable	778,674
Number of Shares, Vested and expected to vest	782,674
Weighted-Average Exercise Price, Outstanding, Beginning Balance | $ / shares	$ 5.51
Weighted-Average Exercise Price, Granted | $ / shares	5.65
Weighted-Average Exercise Price, Exercised | $ / shares	2.83
Weighted-Average Exercise Price, Forfeited or expired | $ / shares	5.65
Weighted-Average Exercise Price, Outstanding, Ending Balance | $ / shares	5.55
Weighted-Average Exercise Price, Exercisable | $ / shares	5.55
Weighted-Average Exercise Price, Vested and expected to vest | $ / shares	$ 5.55
Weighted-Average Remaining Contractual Term, Outstanding	4 years 7 months 21 days
Weighted-Average Remaining Contractual Term, Exercisable	4 years 7 months 13 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	4 years 7 months 21 days
Aggregate Intrinsic Value, Outstanding, Ending balance | $	$ 1,278
Aggregate Intrinsic Value, Exercisable | $	1,278
Aggregate Intrinsic Value, Vested and expected to vest | $	$ 1,278