Shared-Based Compensation - Reconciliation of Option Activity (Detail) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance (in shares) | shares	746,000
Granted (in shares) | shares	57,800
Exercised (in shares) | shares	(27,000)
Forfeitures (in shares) | shares	(4,000)
Ending balance (in shares) | shares	773,000
Options exercisable (in shares) | shares	626,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Beginning balance (in USD per share) | $ / shares	$ 14.33
Granted (in USD per share) | $ / shares	24.41
Exercised (in USD per share) | $ / shares	10.15
Forfeitures (in USD per share) | $ / shares	23.51
Ending balance (in USD share) | $ / shares	15.19
Options exercisable (in USD per share) | $ / shares	$ 13.63
Weighted-Average Remaining Contractual Term, Outstanding	5 years 10 months 24 days
Weighted- Average Remaining Contractual Term, Options exercisable	5 years 2 months 12 days
Aggregate Intrinsic Value, Exercised | $	$ 477
Aggregate Intrinsic Value, Outstanding | $	319
Aggregate Intrinsic Value, Options exercisable | $	$ 1,232