Commitments and Contingencies - Additional Information (Detail)			1 Months Ended							3 Months Ended		9 Months Ended
		Jan. 29, 2018 USD ($)	Oct. 31, 2018 USD ($)	Jul. 31, 2018 USD ($)	May 31, 2018 plaintiff	Apr. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Aug. 31, 2016 lawsuit	May 31, 2016 lawsuit	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Nov. 07, 2018 USD ($)	Dec. 31, 2017 USD ($)
Commitments and Contingencies [Line Items]
Rental expense										$ 4,300,000	$ 4,000,000	$ 12,800,000	$ 11,700,000
Sublease rental income										100,000	100,000.0	200,000	300,000
Minimum rent payments										4,200,000	4,000,000	12,000,000	11,000,000
Security deposit - cash										800,000		800,000
Security deposit - letters of credit										5,500,000		$ 5,500,000
Loan purchase obligation period												2 days
Contingent loan purchase commitment limit										45,100,000		$ 45,100,000			$ 54,200,000
Commitment repurchases												2,400,000	1,700,000
Deposit										9,000,000		9,000,000			9,000,000
Investor Loan Purchase Agreement, Purchases												18,900,000
Principal balance										28,900,000		28,900,000			20,100,000
Fair value										25,800,000		25,800,000			18,200,000
Pledged and restricted to support contingent obligation										800,000		800,000			2,200,000
Maximum exposure										6,000,000		6,000,000			6,000,000
Credit loss coverage reserve										0		0			0
Number of lawsuits | lawsuit								2	2
Preliminary litigation settlement awarded to other party		$ 125,000,000
Litigation settlement to be paid from insurance		$ 47,750,000
Litigation settlement paid by insurance						$ 9,600,000	$ 38,200,000					52,100,000
Litigation settlement paid by the Company				$ 62,500,000		$ 14,750,000
Contingent liabilities (1)										19,089,000		19,089,000			129,887,000
Other assets	[1]									113,896,000		113,896,000			156,278,000
Contingent liabilities paid												146,300,000
Class action and regulatory litigation expense										9,738,000	$ 0	35,500,000	$ 0
Subsequent Event
Commitments and Contingencies [Line Items]
Remaining limit of contingent loan purchase commitment														$ 0
Insurance reimbursements receivable
Commitments and Contingencies [Line Items]
Other assets										$ 0		$ 0			$ 52,119,000
Opt-Out Lawsuits
Commitments and Contingencies [Line Items]
Number of plaintiffs who opted out of settlement of class action lawsuit | plaintiff					2
DOJ Investigation | Subsequent Event
Commitments and Contingencies [Line Items]
Civil money penalty paid			$ 2,000,000
LendingClub Asset Management | SEC Investigation | Subsequent Event
Commitments and Contingencies [Line Items]
Civil money penalty paid			$ 4,000,000

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