Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2016	Mar. 31, 2015
Auction Rate Securities [Member]
Other comprehensive income, net of tax:
Change in unrealized losses on auction-rate securities, net of $0 tax in 2016 and 2015	$ (8)	$ 5
Available-for-sale Securities [Member]
Other comprehensive income, net of tax:
Change in unrealized losses on auction-rate securities, net of $0 tax in 2016 and 2015	218	31
Net income	10,575	5,963
Foreign currency translation adjustments	498	249
Total other comprehensive income, net of tax	(708)	(285)
Comprehensive income	$ 11,283	$ 6,248

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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