CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (UNAUDITED) (in thousands) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 317,401	$ 74,434
Other comprehensive income (loss), net of tax:
Pension liability adjustment	260	(567)
Total other comprehensive income (loss), net of tax	260	(567)
Total comprehensive income	$ 317,661	$ 73,867