Annual report pursuant to Section 13 and 15(d)

Securitization of Receivables - Summary of Certain Transactions with Securitization Trusts (Detail)

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Securitization of Receivables - Summary of Certain Transactions with Securitization Trusts (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]      
Gains on securitizations $ 28,915 $ 10,912 $ 3,873
Securitization Trust [Member]      
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]      
Gains on securitizations 21,000 17,000 8,000
Purchase of receivables securitized 466,000 532,000 286,000
Proceeds from securitizations 487,000 549,000 294,000
Cash received from residual and servicing assets 4,000 2,000 2,000
Securitization Trust [Member] | Residual Assets [Member]      
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]      
Residual and servicing assets included in other assets $ 46,000 $ 19,000 $ 9,000