Shared-Based Compensation - Components of Share-Based Compensation Expense by Type of Award (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 289	$ 1,767	$ 2,623	$ 3,985
Stock Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	173	527	531	1,102
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	388	773	1,244	1,628
Performance Based Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	530	467	1,650	1,255
Change in Estimate of Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ (802)	$ 0	$ (802)	$ 0