Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net income	$ 35,172	$ 35,495	$ 22,898
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	(4,166)	(609)	1,988
Total other comprehensive income (loss), net of tax	(4,345)	(449)	2,085
Comprehensive income	30,827	35,046	24,983
Available-for-sale Securities [Member]
Other comprehensive income (loss), net of tax:
Change in unrealized losses on securities, net of tax	(151)	(19)	(33)
Auction Rate Securities [Member]
Other comprehensive income (loss), net of tax:
Change in unrealized losses on securities, net of tax	$ (28)	$ 179	$ 130