Stock-Based Compensation - Summary of Unvested Option (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Unvested, options beginning balance	402,770
Granted, options	56,150
Vested, options	(142,180)
Forfeited, options	(7,020)
Unvested, options ending balance	309,720	402,770
Unvested , weighted average grant date fair value beginning balance	$ 11.88
Granted, weighted average grant date fair value	15.49	$ 9.99	$ 15.41
Vested, weighted average grant date fair value	12.26	12.95	$ 5.66
Forfeited, weighted average grant date fair value	11.15
Unvested , weighted average grant date fair value ending balance	$ 12.38	$ 11.88