CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net income (loss)	$ (313,142)	$ 104,222	$ 6,531
Other comprehensive loss:
Foreign currency translation	(39)	(9)
Unrealized gain (loss) on marketable securities and long term investment, net of tax	1,615	504	(794)
Reclassification adjustment for realized (gain) loss on marketable securities		178	(1,830)
Defined benefit pension obligations, net of tax	(5,700)	(2,750)
Other comprehensive loss	(4,124)	(2,077)	(2,624)
Comprehensive income (loss)	$ (317,266)	$ 102,145	$ 3,907