Stock Options and Other Equity-Based Incentive Instruments - Summary of Options Outstanding (Detail) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($) $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of options | shares	1,034,850
Weighted average exercise price	$ 18.17
Intrinsic value (in thousands) | $	$ 6,658
Weighted average remaining contractual term (yrs.)	4 years 9 months 18 days
Currently Exercisable [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of options | shares	755,850
Weighted average exercise price	$ 18.52
Intrinsic value (in thousands) | $	$ 4,611
Weighted average remaining contractual term (yrs.)	4 years 1 month 6 days
Currently Not Exercisable [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of options | shares	279,000
Weighted average exercise price	$ 17.23
Intrinsic value (in thousands) | $	$ 2,047
Weighted average remaining contractual term (yrs.)	6 years 9 months 18 days