Debt - Additional Information (Details) (USD $)	12 Months Ended			0 Months Ended	1 Months Ended	3 Months Ended	0 Months Ended	12 Months Ended	0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014 quarter	Oct. 31, 2019	Dec. 31, 2014	Feb. 25, 2011	Dec. 31, 2011	Feb. 04, 2013	Oct. 08, 2010	Oct. 19, 2010
Debt Instrument [Line Items]
Repayments of Long-term Debt	$ 1,264,086,000	$ 4,800,000	$ 216,037,000
Debt Instrument, Basis Spread on Variable Rate	4.50%
LIBOR Rate Floor	1.50%
Base Rate Floor	2.50%
Federal Funds Rate Additional Margin	0.50%
One Month LIBOR Rate Floor	1.50%
One Month LIBOR Rate Additional Margin	1.00%
One Month LIBOR Rate Additional Margin Uplift	3.50%
Upfront Fee on Debt, Percent	1.00%
Debt modification costs	0	1,296,000	0
Series 2014-1, Class A-2 4.227% Fixed Rate Senior Secured Notes
Debt Instrument [Line Items]
Debt Instrument, Face Amount				1,300,000,000
Senior note interest rate	4.227%			4.277%		4.227%
Debt Instrument, Restrictive Covenant, Number of Quarters Used in Leverage Ratio Calculation				4
Ratio of Indebtedness to Net Capital	5.25					5.25
Deferred Finance Costs, Net	23,500,000			24,300,000		23,500,000
Amortization of Financing Costs	800,000
Debt Service Coverage Ratio	4.9
Series 2014-1, Class A-2 4.227% Fixed Rate Senior Secured Notes | Forecast
Debt Instrument [Line Items]
Debt Instrument, Additional Interest on Fixed Rate					5.00%
Series 2014-1 Variable Funding Senior Notes Class A-1
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				100,000,000
Line of Credit Facility, Amount Outstanding	0					0
Debt Instrument, Interest Rate, Effective Percentage	4.45%					4.45%
Line of Credit Facility, Increase (Decrease) in Borrowing Capacity Through the Period						9,600,000
Series 2014-1 Variable Funding Senior Notes Class A-1 | Maximum
Debt Instrument [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	1.00%
Series 2014-1 Variable Funding Senior Notes Class A-1 | Minimum
Debt Instrument [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.50%
Series 2014-1 Variable Funding Senior Notes Class A-1 | Forecast
Debt Instrument [Line Items]
Debt Instrument, Additional Interest on Variable Rate					5.00%
Senior Secured Credit Facility, due Oct 2017
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	150,000,000					150,000,000				250,000,000
Secured credit facility interest rate	3.75%	4.25%				3.75%
Senior Secured Credit Facility	0	467,200,000				0
Mandatory Prepayment of Debt, Percent per Quarter	0.25%
Mandatory Prepayment of Debt, Percent per Annum	1.00%
Amended Senior Secured Revolving Credit Facility
Debt Instrument [Line Items]
Repayments of Long-term Debt				463,600,000
Payments of Debt Restructuring Costs							12,300,000
Payments of Debt Restructuring Costs, Recorded as Additional Discount on Debt							7,400,000
Payments of Debt Restructuring Costs, Recorded as Deferred Financing Costs							800,000
Debt modification costs								4,000,000
Deferred Finance Costs, Net							800,000
Amended Senior Secured Revolving Credit Facility | Maximum
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity							75,000,000.0
Debt Instrument, Basis Spread on Variable Rate							4.50%
LIBOR Rate Floor							1.50%
Base Rate Floor							2.50%
Amended Senior Secured Revolving Credit Facility | Minimum
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity							50,000,000.0
Debt Instrument, Basis Spread on Variable Rate							3.00%
LIBOR Rate Floor							1.25%
Base Rate Floor							2.25%
Second Amended Senior Secured Revolving Credit Facility
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital	5.75					5.75			4.75
Percent of Excess Cash Flow Required For Mandatory Prepayment, Annual Mininum	50.00%					50.00%			50.00%
Second Amended Senior Secured Revolving Credit Facility | Maximum
Debt Instrument [Line Items]
Federal Funds Rate Additional Margin									3.50%
One Month LIBOR Rate Additional Margin									4.50%
Upfront Fee on Debt, Percent									0.75%
Ratio of Indebtedness to Net Capital									5.75
Second Amended Senior Secured Revolving Credit Facility | Minimum
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate									2.75%
LIBOR Rate Floor									1.00%
Base Rate Floor									2.00%
Federal Funds Rate Additional Margin									1.75%
One Month LIBOR Rate Additional Margin									2.75%
Upfront Fee on Debt, Percent									0.50%
Ten Year United States Treasury Bill Rate | Series 2014-1, Class A-2 4.227% Fixed Rate Senior Secured Notes | Forecast
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					2.15%
LIBOR | Series 2014-1 Variable Funding Senior Notes Class A-1
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				2.50%
Federal Funds Rate | Series 2014-1 Variable Funding Senior Notes Class A-1
Debt Instrument [Line Items]
Debt Instrument, Basis Spread Component of Base Rate				0.50%
One Month LIBOR | Series 2014-1 Variable Funding Senior Notes Class A-1
Debt Instrument [Line Items]
Debt Instrument, Basis Spread Component of Base Rate				0.50%
Base Rate | Series 2014-1 Variable Funding Senior Notes Class A-1
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				2.00%
Commercial Paper Funding Rate | Series 2014-1 Variable Funding Senior Notes Class A-1
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				2.50%
First Trigger | Series 2014-1, Class A-2 4.227% Fixed Rate Senior Secured Notes
Debt Instrument [Line Items]
Debt Service Coverage Ratio, Event Trigger Threshold	1.75
Debt Instrument, Restrictive Covenant, Restriction on Net Cash Flow	50.00%
First Trigger | Second Amended Senior Secured Revolving Credit Facility
Debt Instrument [Line Items]
Percent of Excess Cash Flow Required For Mandatory Prepayment, Annual Mininum									25.00%
First Trigger | Second Amended Senior Secured Revolving Credit Facility | Maximum
Debt Instrument [Line Items]
Upfront Fee on Debt, Percent									0.50%
Ratio of Indebtedness to Net Capital	5.75					5.75			5.75
Percent of Excess Cash Flow Required For Mandatory Prepayment, Annual Mininum	25.00%					25.00%
First Trigger | Second Amended Senior Secured Revolving Credit Facility | Minimum
Debt Instrument [Line Items]
Upfront Fee on Debt, Percent									0.375%
Ratio of Indebtedness to Net Capital	5.25					5.25			5.25
Percent of Excess Cash Flow Required For Mandatory Prepayment, Annual Mininum	25.00%					25.00%
Second Trigger | Series 2014-1, Class A-2 4.227% Fixed Rate Senior Secured Notes
Debt Instrument [Line Items]
Debt Service Coverage Ratio, Event Trigger Threshold	1.5
Debt Instrument, Restrictive Covenant, Restriction on Net Cash Flow	100.00%
Second Trigger | Second Amended Senior Secured Revolving Credit Facility
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital	5.25					5.25			5.25
Percent of Excess Cash Flow Required For Mandatory Prepayment, Annual Mininum	0.00%					0.00%			0.00%
Third Trigger | Series 2014-1, Class A-2 4.227% Fixed Rate Senior Secured Notes
Debt Instrument [Line Items]
Debt Service Coverage Ratio, Event Trigger Threshold	1.3
Debt Instrument, Covenant Violation Description	Rapid Amortization
Fourth Trigger | Series 2014-1, Class A-2 4.227% Fixed Rate Senior Secured Notes
Debt Instrument [Line Items]
Debt Service Coverage Ratio, Event Trigger Threshold	1.2
Debt Instrument, Covenant Violation Description	Manager Termination
Fifth Trigger | Series 2014-1, Class A-2 4.227% Fixed Rate Senior Secured Notes
Debt Instrument [Line Items]
Debt Service Coverage Ratio, Event Trigger Threshold	1.1
Debt Instrument, Covenant Violation Description	Default
Term Loan | Senior Secured Credit Facility, due Oct 2017
Debt Instrument [Line Items]
Debt Instrument, Face Amount										900,000,000
Revolving Credit Facility
Debt Instrument [Line Items]
Percent of Excess Cash Flow Required For Mandatory Prepayment, Annual Mininum											50.00%
Revolving Credit Facility | Maximum
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital											5.75
Revolving Credit Facility | Senior Secured Credit Facility, due Oct 2017
Debt Instrument [Line Items]
Debt Instrument, Face Amount										50,000,000
Revolving Credit Facility | First Trigger
Debt Instrument [Line Items]
Percent of Excess Cash Flow Required For Mandatory Prepayment, Annual Mininum											75.00%
Revolving Credit Facility | First Trigger | Maximum
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital											5.75
Revolving Credit Facility | First Trigger | Minimum
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital											5.25
Revolving Credit Facility | Second Trigger
Debt Instrument [Line Items]
Percent of Excess Cash Flow Required For Mandatory Prepayment, Annual Mininum											100.00%
Revolving Credit Facility | Second Trigger | Minimum
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital											5.25
Letter of Credit | Senior Secured Credit Facility, due Oct 2017
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity										$ 50,000,000