Loans, Loans Held For Sale, Notes, Certificates and Secured Borrowings and Loan Servicing Rights - Fair value on a recurring basis (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	[1],[2]	$ 2,932,325	$ 4,295,121
Fair value	[1]	235,825	9,048
Fair value	[1]	2,954,768	4,320,895
Fair Value, Measurements, Recurring | Loans Held For Investment
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Aggregate principal balance outstanding		3,141,391	4,547,138
Net fair value adjustments		(209,066)	(252,017)
Fair value		2,932,325	4,295,121
Fair Value, Measurements, Recurring | Notes, Certificates and Secured Borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Aggregate principal balance outstanding		3,161,080	4,572,912
Net fair value adjustments		(206,312)	(252,017)
Fair value		2,954,768	4,320,895
Loans Invested in by Company | Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Aggregate principal balance outstanding		613,652	27,860
Net fair value adjustments		(16,597)	(1,949)
Loans Receivable and Loans Held for Sale, Fair Value Disclosure		597,055	25,911
Loans Invested in by Company | Fair Value, Measurements, Recurring | Loans Held For Investment
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Aggregate principal balance outstanding		371,379	18,515
Net fair value adjustments		(10,149)	(1,652)
Fair value		361,230	16,863
Loans Invested in by Company | Fair Value, Measurements, Recurring | Loans Held For Sale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Aggregate principal balance outstanding		242,273	9,345
Net fair value adjustments		(6,448)	(297)
Fair value		$ 235,825	$ 9,048

[1] Includes amounts in consolidated variable interest entities (VIEs) presented separately in the table below.

[2] Prior period amounts have been reclassified to conform to the current period presentation. See “Notes to Consolidated Financial Statements – Note 1. Basis of Presentation” for additional information.