Income Taxes - Valuation Allowance (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Income Tax Disclosure [Abstract]
Increase in valuation allowance before consideration of the Tax Act	$ 246,037
Increase in valuation allowance before consideration of the Tax Act	48,531
Total increase in valuation allowance	294,568
Tax Act rate change - decrease in valuation allowance	(172,235)
Impact on net operating loss usage	(50,551)
Total decrease in valuation allowance due to Tax Act	(222,786)
Total increase in valuation allowance	$ 71,782