Fair Value of Financial Instruments Measured at Fair Value - Additional Information about Servicing Assets and Liabilities Measured Using Different Market Servicing Rates and Different Prepayment (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market servicing rates (% per annum on unpaid principal balance)	0.50%		0.50%
Cumulative prepayment rates	21.50%		20.00%
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market servicing rates (% per annum on unpaid principal balance)	0.50%		0.50%
Changes in fair value, included in servicing fees	$ (491)	$ (112)
Changes in fair value, included in servicing fees	(988)	(227)
Cumulative prepayment rates	21.50%		20.00%
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	(1,299)		(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	1,537		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	1,365		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	(1,471)		(1,366)
25% increase in cumulative prepayments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Changes in fair value, included in servicing fees	(120)		(65)
25% increase in cumulative prepayments | 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	(277)		(228)
25% decrease in cumulative prepayments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Changes in fair value, included in servicing fees	126		67
25% decrease in cumulative prepayments | 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	$ 285		231
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market servicing rates (% per annum on unpaid principal balance)	0.40%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Market servicing rates (% per annum on unpaid principal balance)	0.70%