Fair Value Measurements - Fair Value and Carrying Value of Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	May 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	$ 286,881	$ 385,410
2013 8.00% Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	$ 1,392	1,376
Loan interest rate	8.00%		8.00%
2013 8.00% Notes | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	$ 1,392	1,376
2013 8.00% Notes | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value	$ 1,241	$ 1,122