Income Taxes - Income Tax Benefit (Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current income tax benefit (expense)
Federal	$ 0	$ 0	$ 0
State	(45)	94	0
Foreign	421	(1,036)	(225)
Current income tax benefit (expense)	376	(942)	(225)
Deferred income tax benefit (expense)
Federal	22,619	2,113	24,151
State	10,282	6,936	9,736
Foreign	2,674	(2,560)	1,035
Change in enacted tax rates	(123,289)	0	0
Net operating loss carryforwards created	17,466	105,165	88,110
Deferred income tax benefit (expense)	(70,248)	111,654	123,032
Income tax benefit (expense) before valuation allowances	(69,872)	110,712	122,807
Deferred tax valuation allowances	100,362	(114,980)	(114,106)
Income tax benefit (expense)	$ 30,490	$ (4,268)	$ 8,701