CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 16,716	$ 13,672	$ 29,079	$ 24,575
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments, net of $0 tax in the three and six months ended June 30, 2014 and 2013 (Note 2)	17	(13)	11	(164)
Unrealized gain (loss) on marketable securities, net of $0 tax in the three and six months ended June 30, 2014 and 2013 (Note 2)	92	(204)	239	(258)
Amortization of defined benefit pension items, net of tax of $4 and $4 in the quarters ended June 30, 2014 and 2013, respectively, and $8 and $8 in the six months ended June 30, 2014 and 2013, respectively (Note 2)	16	14	30	28
Total other comprehensive income (loss)	125	(203)	280	(394)
Total comprehensive income	$ 16,841	$ 13,469	$ 29,359	$ 24,181