Fair Value of Assets and Liabilities - Additional Information about Servicing Assets and Liabilities Measured Using Different Market Servicing Rates and Different Prepayment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Base market servicing rates (% per annum on unpaid principal balance)(1)			0.50%		0.50%
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Base market servicing rates (% per annum on unpaid principal balance)(1)			0.50%		0.50%
Changes in fair value, included in servicing fees	$ (1,436)	$ (182)	$ (2,467)	$ (841)
Changes in fair value, included in servicing fees	$ (1,839)	$ (833)	(3,919)	$ (688)
Servicing rate increase to 0.60%
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Changes in fair value, included in servicing fees			(2,566)		$ (915)
Servicing rate increase to 0.60% | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Changes in fair value, included in servicing fees			1,764		1,416
Servicing rate decrease to 0.40%
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Changes in fair value, included in servicing fees			2,682		965
Servicing rate decrease to 0.40% | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Changes in fair value, included in servicing fees			$ (1,649)		$ (1,366)
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Base market servicing rates (% per annum on unpaid principal balance)(1)			0.40%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Base market servicing rates (% per annum on unpaid principal balance)(1)			0.75%