CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 193,468	$ 69,984	$ 27,609
Other comprehensive income:
Foreign currency translation adjustments, net of $0 tax in 2019, 2018 and 2017	(518)	(236)	79
Unrealized gain (loss) on marketable securities, net of $0 tax in 2019, 2018 and 2017	849	161	(207)
Unrealized actuarial gain (loss) on pension benefits, net of tax of $497, ($144), and ($194) in 2019, 2018 and 2017, respectively	(1,772)	525	699
Total other comprehensive income (loss)	(1,441)	450	571
Total comprehensive income	192,027	70,434	28,180
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