Changes in Accumulated Balances of Other Comprehensive Income (Loss), Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ 211,551
Other comprehensive income, net of taxes	$ 77	$ 39	296	$ 452
Ending balance	238,956		238,956
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(278)	(6)	(497)	(419)
Other comprehensive income (loss) before reclassifications	79	100	438	610
Amounts reclassified from accumulated other comprehensive income (loss)	(2)	(61)	(142)	(158)
Other comprehensive income, net of taxes	77	39	296	452
Ending balance	(201)	33	(201)	33
Unrealized gains (losses) on available-for-sale marketable securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(278)	(32)	(502)	(427)
Other comprehensive income (loss) before reclassifications	82	34	277	416
Amounts reclassified from accumulated other comprehensive income (loss)	(5)		24	13
Other comprehensive income, net of taxes	77	34	301	429
Ending balance	(201)	2	(201)	2
Unrealized gains (losses) on cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		26	5	8
Other comprehensive income (loss) before reclassifications	(3)	66	161	194
Amounts reclassified from accumulated other comprehensive income (loss)	$ 3	(61)	(166)	(171)
Other comprehensive income, net of taxes		5	$ (5)	23
Ending balance		$ 31		$ 31