Commitments and Contingencies - Additional Information (Detail)			1 Months Ended						3 Months Ended			6 Months Ended
		Jan. 29, 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	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Aug. 08, 2018 USD ($)
Commitments and Contingencies [Line Items]
Rental expense									$ 4,300,000		$ 4,000,000	$ 8,600,000	$ 7,800,000
Sublease rental income									77,000		100,000.0	200,000.0	200,000.0
Minimum rent payments									3,800,000		3,400,000	7,800,000	7,000,000
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									50,900,000	$ 54,200,000		$ 50,900,000
Commitment repurchases												2,000,000	1,100,000
Deposit									9,000,000	9,000,000		9,000,000
Investor Loan Purchase Agreement, Purchases												9,800,000
Principal balance									23,900,000	20,100,000		23,900,000
Fair value									21,500,000	18,200,000		21,500,000
Pledged and restricted to support contingent obligation									900,000	2,200,000		900,000
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						47,750,000
Litigation settlement paid by the Company					$ 14,750,000							14,750,000
Contingent liabilities									89,601,000	129,887,000		89,601,000
Other assets	[1]								102,396,000	156,278,000		102,396,000
Class action settlement and regulatory litigation expense									12,262,000	77,250,000	$ 0	25,762,000	$ 0
Subsequent Event
Commitments and Contingencies [Line Items]
Remaining limit of contingent loan purchase commitment														$ 0
Litigation settlement paid by the Company			$ 62,500,000
Insurance reimbursements receivable
Commitments and Contingencies [Line Items]
Other assets									$ 0	$ 52,119,000		$ 0
Opt-Out Lawsuits
Commitments and Contingencies [Line Items]
Number of plaintiffs who opted out of settlement of class action lawsuit | plaintiff				2

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