CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 47,890	$ 39,147	$ 59,544
Other comprehensive income:
Foreign currency translation adjustments, net of $0 tax in 2016, 2015 and 2014	(384)	(191)	(79)
Unrealized loss on marketable securities, net of $0 tax in 2016, 2015 and 2014	(123)	(180)	(127)
Unrealized actuarial loss on pension benefits, net of tax of $98, $96 and $128 in 2016, 2015 and 2014, respectively	(352)	(344)	(460)
Total other comprehensive loss	(859)	(715)	(666)
Total comprehensive income	47,031	38,432	58,878
Foreign currency translation adjustment, tax	0	0	0
Unrealized gain on marketable securities, tax	0	0	0
Unrealized actuarial loss on pension benefits, tax	$ 98	$ 96	$ 128