Income Taxes - Provision (benefit) for income taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]
Federal	$ 42,600	$ 60,800	$ 67,300
State	5,100	6,400	8,000
Foreign	2,900	2,300	2,400
Current Income Tax Expense	50,600	69,500	77,700
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Federal	(140,700)	(10,600)	(13,600)
State	(4,700)	(3,800)	(400)
Deferred income tax expense (benefit)	(145,402)	(14,434)	(13,987)
(Benefit) provision for income taxes	$ (94,835)	$ 55,130	$ 63,726