Fair Value of Assets and Liabilities - Loans, Loan Servicing Rights, Related Notes and Certificates (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	$ 4,068,974	$ 2,798,505
Securities available for sale:	338,519	0
Servicing assets	7,249	2,181
Total assets	4,414,742	2,800,686
Notes and certificates	4,095,481	2,813,618
Servicing liabilities	4,394	3,973
Total liabilities	4,099,875	2,817,591
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	250,113
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	54,959
U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	20,603
Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	5,843
Other securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	7,001
Level 1 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	0	0
Securities available for sale:	0
Servicing assets	0	0
Total assets	0	0
Notes and certificates	0	0
Servicing liabilities	0	0
Total liabilities	0	0
Level 1 Inputs | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	0
Level 1 Inputs | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	0
Level 1 Inputs | U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	0
Level 1 Inputs | Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	0
Level 1 Inputs | Other securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	0
Level 2 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	0	0
Securities available for sale:	338,519
Servicing assets	0	0
Total assets	338,519	0
Notes and certificates	0	0
Servicing liabilities	0	0
Total liabilities	0	0
Level 2 Inputs | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	250,113
Level 2 Inputs | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	54,959
Level 2 Inputs | U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	20,603
Level 2 Inputs | Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	5,843
Level 2 Inputs | Other securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	7,001
Level 3 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	4,068,974	2,798,505
Securities available for sale:	0
Servicing assets	7,249	2,181
Total assets	4,076,223	2,800,686
Notes and certificates	4,095,481	2,813,618
Servicing liabilities	4,394	3,973
Total liabilities	4,099,875	$ 2,817,591
Level 3 Inputs | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	0
Level 3 Inputs | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	0
Level 3 Inputs | U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	0
Level 3 Inputs | Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	0
Level 3 Inputs | Other securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale:	$ 0