Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Net income	$ 7,899	$ 6,397	$ 13,862	$ 15,415
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	105	176	354	(420)
Total other comprehensive income (loss), net of tax	90	188	375	(420)
Comprehensive income	7,989	6,585	14,237	14,995
Available-for-sale Securities [Member]
Other comprehensive income (loss), net of tax:
Change in unrealized losses on securities, net of tax	4	7	35	12
Auction Rate Securities [Member]
Other comprehensive income (loss), net of tax:
Change in unrealized losses on securities, net of tax	$ (19)	$ 5	$ (14)	$ (12)