Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net earnings (loss)	$ (105,907)	$ (11,531)	$ (7,093)	$ (16,983)	$ 29,330	$ (3,277)	$ (3,273)	$ (15,248)	$ (141,514)	$ 7,532	$ (26,680)
Net unrealized gain (loss) on short-term investments									364	310	241
Changes in pension plan assets and benefit obligations									(1)	(3)	(39)
Tax effect of the above-listed adjustments									(85)	(109)	(113)
Currency translation adjustment									(3,950)	0	0
Total comprehensive income (loss)									$ (145,186)	$ 7,730	$ (26,591)