CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 16,111	$ 16,654	$ 45,190	$ 41,229
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments, net of $0 tax in the three and nine months ended September 30, 2014 and 2013 (Note 2)	(53)	118	(42)	(46)
Unrealized gain (loss) on marketable securities, net of $0 tax in the three and nine months ended September 30, 2014 and 2013 (Note 2)	(246)	196	(7)	(62)
Amortization of defined benefit pension items, net of tax of $4 and $4 in the quarters ended September 30, 2014 and 2013, respectively, and $12 and $12 in the nine months ended September 30, 2014 and 2013, respectively (Note 2)	15	15	45	43
Total other comprehensive income (loss)	(284)	329	(4)	(65)
Total comprehensive income	$ 15,827	$ 16,983	$ 45,186	$ 41,164