Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
ODAST II Agreement | Secured Debt
Debt Instrument [Line Items]
Weighted Average Interest Rate at September 30, 2017	4.70%
Debt	$ 250,000	$ 250,000
ODART Agreement | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at September 30, 2017	3.90%
Debt	$ 123,498	133,767
RAOD Agreement | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at September 30, 2017	3.70%
Debt	$ 71,119	99,985
ODAF I Agreement | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at September 30, 2017	8.50%
Debt	$ 81,633	100,000
ODAC Agreement | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at September 30, 2017	8.50%
Debt	$ 76,321	65,486
PORT II Agreement | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at September 30, 2017	3.70%
Debt	$ 67,296	52,397
Other Agreements | Revolving Credit Facility
Debt Instrument [Line Items]
Debt	39,385	30,887
Funding debt
Debt Instrument [Line Items]
Debt	709,252	732,522
Deferred Debt Issuance Cost	(6,254)	(5,883)
Total	702,998	726,639
Corporate debt
Debt Instrument [Line Items]
Total	$ 17,180	27,966
Corporate debt | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted Average Interest Rate at September 30, 2017	5.50%
Debt	$ 17,200	28,000
Deferred Debt Issuance Cost	$ (20)	$ (34)