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Debt - Senior Notes - Narrative (Details) - USD ($)
Mar. 31, 2017
Apr. 29, 2015
Dec. 31, 2017
Dec. 31, 2016
Apr. 01, 2016
Dec. 31, 2015
Dec. 31, 2014
Debt Instrument [Line Items]              
Debt financing costs     $ 900,000 $ 17,200,000   $ 1,500,000 $ 200,000
Unsecured Senior Notes              
Debt Instrument [Line Items]              
Debt instrument, interest rate   5.50%     6.50%    
Purchase price percentage if debt covenants are not certified   100.00%          
Legal fees $ 100,000            
Consent fee $ 200,000   200,000 300,000.0 $ 300,000 0  
Unsecured Senior Notes | 5.50% Senior Notes              
Debt Instrument [Line Items]              
Debt instrument, face amount   $ 55,000,000.0          
Debt instrument, interest rate   5.50%          
Proceeds from issuance of long-term debt   $ 53,500,000          
Debt financing costs   $ 1,500,000          
Accrued unpaid interest     $ 600,000 $ 600,000   $ 500,000  
Unsecured Senior Notes | 5.50% Senior Notes | Before May 1, 2016              
Debt Instrument [Line Items]              
Redemption price, percentage   101.00%          
Unsecured Senior Notes | 5.50% Senior Notes | May 1, 2016 through October 31, 2016              
Debt Instrument [Line Items]              
Redemption price, percentage   101.00%