Stock-Based Compensation - Stock Options (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Contractual term	10 years
Total Stock Options
Options outstanding, beginning balance (in shares)	565,425
Options granted (in shares)	0
Options exercised (in shares)	(192,550)	(465,232)	(40,976)
Options cancelled and expired (in shares)	(15,800)
Options outstanding, ending balance (in shares)	357,075	565,425
Vested and expected to vest (in shares)	357,075
Exercisable (in shares)	353,049
Weighted- Average Exercise Price
Options outstanding, beginning balance, weighted average exercise price (in dollars per share)	$ 13.65
Options granted, weighted average exercise price (in dollars per share)	0.00
Options exercised, weighted average exercise price (in dollars per share)	5.98
Options cancelled and expired, weighted average exercise price (in dollars per share)	20.44
Options outstanding, ending balance, weighted average exercise price (in dollars per share)	17.50	$ 13.65
Vested and expected to vest, weighted average exercise price (in dollars per share)	17.50
Exercisable, weighted average exercise price (in dollars per share)	$ 17.56
Stock Option Activity, Additional Disclosures
Options outstanding, weighted average remaining contractual term (in years)	4 years 4 months 24 days
Vested and expected to vest, weighted average remaining contractual term (in years)	4 years 4 months 24 days
Exercisable, weighted average remaining contractual term (in years)	4 years 4 months 24 days
Options outstanding, aggregate intrinsic value	$ 535,427
Vested and expected to vest, aggregate intrinsic value	535,427
Exercisable, aggregate intrinsic value	522,423
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	$ 2,400	$ 5,100	$ 200