Consolidated Statements of Cash Flows - USD ($)		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Cash Flows from Operating Activities:
Consolidated net loss		$ (154,045,000)		$ (145,969,000)		$ (4,995,000)
Adjustments to reconcile consolidated net loss to net cash (used for) provided by operating activities:
Net fair value adjustments	[1]	30,817,000		2,949,000		(14,000)
Change in fair value of loan servicing liabilities		(2,346,000)		(4,498,000)		(5,194,000)
Change in fair value of loan servicing assets		23,172,000		5,403,000		3,803,000
Stock-based compensation, net		70,983,000		69,244,000		51,222,000
Excess tax benefit from share-based awards		0		176,000		(738,000)
Goodwill impairment		0		37,050,000		0
Depreciation and amortization		46,208,000		29,882,000		21,578,000
(Gain) Loss on sales of loans		(38,850,000)		(13,175,000)		(4,885,000)
Other, net		2,744,000		1,791,000		661,000
Purchase of loans held for sale		(6,008,943,000)		(4,742,538,000)		(3,358,611,000)
Principal payments received on loans held for sale		54,107,000		4,380,000		0
Proceeds from sales of whole loans		5,172,941,000		4,731,831,000		3,358,611,000
Purchase of loans held for sale by consolidated VIE		(706,003,000)		0		0
Proceeds from sale of securities by consolidated VIE, net of underwriting fees and costs		853,788,000		0		0
Net change in operating assets and liabilities:
Accrued interest receivable, net		6,293,000		(2,218,000)		(13,819,000)
Other assets		(71,625,000)		(10,140,000)		(15,857,000)
Due from related parties		420,000		179,000		(188,000)
Accounts payable		(1,913,000)		5,582,000		(598,000)
Accrued interest payable		(10,582,000)		3,330,000		13,280,000
Accrued expenses and other liabilities		142,020,000		27,286,000		30,485,000
Net cash (used for) provided by operating activities		(590,814,000)		545,000		74,741,000
Cash Flows from Investing Activities:
Purchase of loans		(1,738,710,000)		(2,732,669,000)		(3,865,565,000)
Principal payments received on loans		2,397,565,000		2,393,354,000		1,804,719,000
Proceeds from recoveries and sales of charged-off loans		48,256,000		37,277,000		26,256,000
Proceeds from sales of whole loans		112,767,000		26,825,000		0
Purchases of securities available for sale		(139,770,000)		(75,983,000)		(419,173,000)
Proceeds from sales, maturities, redemptions and paydowns of securities available for sale		356,608,000		87,158,000		120,420,000
Proceeds from paydowns of asset-backed securities related to Company-sponsored securitizations and CLUB Certificate transactions		6,472,000		0		0
Investment in Cirrix Capital		0		(10,000,000)		0
Net change in restricted cash		(64,760,000)		(97,077,000)		(33,970,000)
Purchases of property, equipment and software, net		(44,615,000)		(51,842,000)		(39,387,000)
Net cash provided by (used for) investing activities		933,813,000		(422,957,000)		(2,406,700,000)
Cash Flows from Financing Activities:
Change in payable to investors		17,426,000		52,722,000		34,421,000
Proceeds from issuance of notes and certificates		1,720,884,000		2,681,109,000		3,861,995,000
Proceeds from secured borrowings		280,495,000		22,274,000		0
Repayments of secured borrowings		(42,834,000)		(22,274,000)		0
Principal payments on and retirements of notes and certificates		(2,737,029,000)		(2,381,372,000)		(1,800,859,000)
Payments on notes and certificates from recoveries/sales of related charged-off loans		(47,914,000)		(36,785,000)		(26,143,000)
Proceeds from issuance of securitization notes and residual certificates		313,486,000		0		0
Proceeds from revolving credit facilities		283,100,000		0		0
Principal payments on revolving credit facilities		(251,000,000)		0		0
Payment for debt issuance costs		(5,099,000)		0		(1,296,000)
Repurchases of common stock		0		(19,485,000)		0
Proceeds from exercise of warrants to acquire common stock		0		17,000		3,000
Proceeds from stock option exercises and other		14,562,000		13,209,000		11,670,000
Excess tax benefit from share-based awards		0		(176,000)		738,000
Proceeds from issuance of common stock for ESPP		5,611,000		5,244,000		5,091,000
Purchase of noncontrolling interests in consolidated VIE		(6,307,000)		0		0
Return of capital to noncontrolling interests in consolidated VIE		(2,191,000)		0		0
Dividends paid to noncontrolling interests in consolidated VIE		(72,000)		0		0
Other financing activities		0		0		90,000
Net cash (used for) provided by financing activities		(456,882,000)		314,483,000		2,085,710,000
Net Decrease in Cash and Cash Equivalents		(113,883,000)		(107,929,000)		(246,249,000)
Cash and Cash Equivalents, Beginning of Period		515,602,000	[2]	623,531,000		869,780,000
Cash and Cash Equivalents, End of Period		401,719,000	[2]	515,602,000	[2]	623,531,000
Supplemental Cash Flow Information:
Cash paid for interest		581,435,000		684,775,000		536,448,000
Accruals for property, equipment and software		710,000		1,089,000		2,975,000
Beneficial interests retained by consolidated VIE		54,955,000		0		0
Transfer of whole loans to redeem certificates		130,223,000		3,862,000		0
Noncontrolling interests’ contribution of beneficial interests in consolidated VIE		7,722,000		0		0
Issuance of payable to securitization residual certificate holders		$ 1,549,000		$ 0		$ 0

[1] 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.

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