Annual report pursuant to Section 13 and 15(d)

Income Taxes - Narrative (Details)

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Income Taxes - Narrative (Details) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Tax Credit Carryforward [Line Items]      
Effective income tax rate reconciliation, at federal statutory income tax rate, percent 35.00%    
Deferred tax assets, decrease in valuation allowance $ 9,722,000    
Deferred tax assets, decrease in valuation allowance, Tax Cuts And Jobs Act Of 2017 55,704,000    
Change in valuation allowance affecting tax expense 39,499,000 $ 26,892,000 $ 24,149,000
Deferred tax assets, change in valuation allowance related to state tax and other adjustment to deferred taxes 6,483,000    
Operating loss carryforwards, limitation as per IRC 129,521,000    
Alternative minimum tax credit carryforwards 426,000    
Accrued interest and penalties related to uncertain tax positions 86,000    
Expected increase in uncertain tax position in next twelve months 0    
Expected decrease in uncertain tax position in next twelve months 0    
Federal      
Tax Credit Carryforward [Line Items]      
Operating loss carryforwards 679,925,000    
State      
Tax Credit Carryforward [Line Items]      
Operating loss carryforwards 226,509,000    
Tax credit carryforward $ 883,000