Stock Based Compensation (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Share based Compensation Allocation of Recognized Period Cost [Line Items]
Total stock based compensation expense	$ 862	$ 700	$ 2,815	$ 2,067
Expected vesting percent					50.00%
2015 LTIP (performance-based)
Share based Compensation Allocation of Recognized Period Cost [Line Items]
Total stock based compensation expense	388	584	1,385	1,737
Time-based awards (including 2017 LTIP)
Share based Compensation Allocation of Recognized Period Cost [Line Items]
Total stock based compensation expense	358	0	1,073	0
ESPP
Share based Compensation Allocation of Recognized Period Cost [Line Items]
Total stock based compensation expense	16	9	46	9
Board Of Directors | Board of Directors restricted stock | Restricted Stock
Share based Compensation Allocation of Recognized Period Cost [Line Items]
Total stock based compensation expense	$ 100	$ 107	$ 311	$ 321