Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Net income	$ 11,201	$ 11,221	$ 25,063	$ 26,635
Other comprehensive loss, net of tax:
Foreign currency translation adjustments	(3,132)	(98)	(2,778)	(518)
Total other comprehensive loss, net of tax	(3,102)	(179)	(2,727)	(599)
Comprehensive income	8,099	11,042	22,336	26,036
Available-for-sale Securities [Member]
Other comprehensive loss, net of tax:
Change in unrealized losses on securities, net of tax	41	(28)	76	(16)
Auction Rate Securities [Member]
Other comprehensive loss, net of tax:
Change in unrealized losses on securities, net of tax	$ (11)	$ (53)	$ (25)	$ (65)