CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 69,984	$ 27,609	$ 48,898
Other comprehensive income:
Foreign currency translation adjustments, net of $0 tax in 2018, 2017 and 2016	(236)	79	(384)
Unrealized gain (loss) on marketable securities, net of $0 tax in 2018, 2017 and 2016	161	(207)	(123)
Unrealized actuarial gain (loss) on pension benefits, net of tax of ($144), ($194), and $98 in 2018, 2017 and 2016, respectively	525	699	(352)
Total other comprehensive income (loss)	450	571	(859)
Total comprehensive income	70,434	28,180	48,039
Foreign currency translation adjustment, tax	0	0	0
Unrealized gain on marketable securities, tax	0	0	0
Unrealized actuarial gain (loss) on pension benefits, tax	$ (144)	$ (198)	$ 98