Stock-Based Compensation - Summary of Share Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock-based compensation expense:
Total stock-based compensation expense	$ 1,271	$ 1,454	$ 3,074	$ 4,349
Time-based Restricted Units [Member]
Stock-based compensation expense:
Total stock-based compensation expense	582	631	1,678	1,847
Performance-based Restricted Units [Member]
Stock-based compensation expense:
Total stock-based compensation expense	$ 689	$ 823	$ 1,396	$ 2,502