Stock-Based Compensation - Summary of Share Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Stock-based compensation expense:
Total stock-based compensation expense	$ 1,261	$ 1,406	$ 1,816	$ 2,896
Time-based Restricted Units [Member]
Stock-based compensation expense:
Total stock-based compensation expense	556	597	1,111	1,216
Performance-based Restricted Units [Member]
Stock-based compensation expense:
Total stock-based compensation expense	$ 705	$ 809	$ 705	$ 1,680