Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Income tax receivable	$ 8,371,000	$ 27,057,000
Income tax benefit due to change in tax rate	33,500,000
Valuation allowance	4,993,000	5,135,000
Unrecognized tax benefits	1,700,000	1,700,000
Unrecognized tax benefits that would impact effective tax rate	0	0
Unrecognized tax benefits, period increase (decrease)	0	0
Unrecognized tax benefits, income tax penalties accrued	0	0
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	0	0
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	391,700,000	427,300,000
ATM Credit | Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Tax credit carryforward		$ 13,500,000
Amount of AMT credit utilized	5,100,000
Income tax receivable	8,400,000
Tax Year 2014
Operating Loss Carryforwards [Line Items]
Federal income tax refund received	21,900,000
Tax Year 2016
Operating Loss Carryforwards [Line Items]
Federal income tax refund received	$ 4,400,000