Income Taxes - Impact of Tax Cuts and Jobs Act (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Income Tax Disclosure [Abstract]
Rate change - decrease in net deferred tax assets	$ 108,070
Rate change - decrease in valuation allowance	(172,235)
Impact on net operating loss usage	(50,551)
Reduction of deferred tax asset - AMT credits	2,361
Total impact of the Tax Act on the Company's deferred taxes position	(112,355)
Realization of AMT credits	(2,361)
Total	$ (114,716)