Accumulated Other Comprehensive Loss - Summary of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 87,500	$ 77,884	$ 68,207
Ending Balance	109,770	87,500	77,884
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(4,583)	(4,049)	(2,365)
Other comprehensive income (loss) before reclassifications	2,294	(534)	(1,684)
Amounts reclassified from accumulated other comprehensive loss	0	0	0
Ending Balance	$ (2,289)	$ (4,583)	$ (4,049)