Income Taxes - Net Operating Loss Carryforwards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards
Deferred tax assets, valuation allowance	$ 67,630	$ 90,052
Deferred tax asset, change in valuation allowance amount	(22,500)	(2,800)	$ 4,400
Federal
Operating Loss Carryforwards
Net operating loss (“NOL”) carryforwards	$ 189,800	155,500
Federal | Earliest Tax Year
Operating Loss Carryforwards
Operating loss carryforwards expiration year	2021
Federal | Latest Tax Year
Operating Loss Carryforwards
Operating loss carryforwards expiration year	2037
State
Operating Loss Carryforwards
Net operating loss (“NOL”) carryforwards	$ 65,400	$ 62,600
State | Earliest Tax Year
Operating Loss Carryforwards
Operating loss carryforwards expiration year	2019
State | Latest Tax Year
Operating Loss Carryforwards
Operating loss carryforwards expiration year	2037