Accumulated Other Comprehensive Income (Loss) - Changes in Balances of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 315,117	$ 231,963
Other comprehensive income (loss) before reclassifications	(550)	1,958
Amounts reclassified to net income (loss)	(257)	(201)
Total other comprehensive (loss) income, net of tax	(807)	1,757
Ending balance	338,261	272,944
Unrealized Gain (Loss) on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	160	(1,065)
Other comprehensive income (loss) before reclassifications	(154)	1,930
Amounts reclassified to net income (loss)	(257)	(201)
Total other comprehensive (loss) income, net of tax	(411)	1,729
Ending balance	(251)	664
Unrealized Gain (Loss) on Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(615)	(413)
Other comprehensive income (loss) before reclassifications	(396)	28
Amounts reclassified to net income (loss)	0	0
Total other comprehensive (loss) income, net of tax	(396)	28
Ending balance	(1,011)	(385)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(455)	(1,478)
Ending balance	$ (1,262)	$ 279