Shared-Based Compensation - Components of Share-Based Compensation Expense by Type of Award (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 1,078	$ 1,066	$ 2,334	$ 2,218
Stock Option Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	152	194	358	575
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	397	395	856	855
Performance Based Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 529	$ 477	$ 1,120	$ 788