Shared-Based Compensation - Reconciliation of Option Activity (Detail) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options [Abstract]
Beginning balance | shares		746,000
Granted | shares	55,300	55,300
Exercised | shares		(27,000)
Ending balance | shares	774,000	774,000
Options exercisable | shares	625,000	625,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Beginning balance | $ / shares		$ 14.33
Granted | $ / shares		24.55
Exercised | $ / shares		10.15
Ending balance | $ / shares	$ 15.21	15.21
Options exercisable | $ / shares	$ 13.61	$ 13.61
Weighted-Average Remaining Contractual Term, Outstanding		6 years 1 month 6 days
Weighted- Average Remaining Contractual Term, Options exercisable		5 years 4 months 24 days
Aggregate Intrinsic Value, Exercised | $		$ 274
Aggregate Intrinsic Value, Outstanding | $	$ 2,861	2,861
Aggregate Intrinsic Value, Options exercisable | $	$ 3,304	$ 3,304