Accumulated Other Comprehensive Income (Loss) - Changes in Balances of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ 315,117	$ 231,963
Other comprehensive income (loss) before reclassifications	$ (2,035)	$ 1,218	(2,585)	3,176
Amounts reclassified to net income (loss)	335	(777)	78	(978)
Total other comprehensive (loss) income, net of tax	(1,700)	441	(2,507)	2,198
Ending balance	328,435	287,115	328,435	287,115
Unrealized Gain (Loss) on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(251)	664	160	(1,065)
Other comprehensive income (loss) before reclassifications	(2,202)	1,196	(2,356)	3,126
Amounts reclassified to net income (loss)	335	(777)	78	(978)
Total other comprehensive (loss) income, net of tax	(1,867)	419	(2,278)	2,148
Ending balance	(2,118)	1,083	(2,118)	1,083
Unrealized Gain (Loss) on Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(1,011)	(385)	(615)	(413)
Other comprehensive income (loss) before reclassifications	167	22	(229)	50
Amounts reclassified to net income (loss)	0	0	0	0
Total other comprehensive (loss) income, net of tax	167	22	(229)	50
Ending balance	(844)	(363)	(844)	(363)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(1,262)	279	(455)	(1,478)
Ending balance	$ (2,962)	$ 720	$ (2,962)	$ 720