Finance Receivables, Credit Quality Information, and Allowance for Credit Losses - Tabular Disclosure of Impaired Financing Receivables (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired receivables specifically evaluated	$ 21,663	$ 17,230
Finance receivables evaluated collectively	866,413	800,233
Finance receivables	888,076	817,463	$ 774,856
Impaired receivables in nonaccrual status	3,211	2,049
Amount of the specific reserve for impaired accounts	8,429	3,766
Amount of the general component of the allowance	46,871	45,144
Small Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired receivables specifically evaluated	6,840	5,094
Finance receivables evaluated collectively	407,601	370,678
Finance receivables	414,441	375,772	363,262
Impaired receivables in nonaccrual status	1,083	719
Amount of the specific reserve for impaired accounts	3,102	1,190
Amount of the general component of the allowance	21,959	23,559
Large Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired receivables specifically evaluated	13,438	10,303
Finance receivables evaluated collectively	397,373	336,915
Finance receivables	410,811	347,218	308,642
Impaired receivables in nonaccrual status	1,824	1,117
Amount of the specific reserve for impaired accounts	4,662	2,183
Amount of the general component of the allowance	20,645	15,365
Automobile Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired receivables specifically evaluated	1,256	1,724
Finance receivables evaluated collectively	31,066	59,699
Finance receivables	32,322	61,423	71,666
Impaired receivables in nonaccrual status	251	185
Amount of the specific reserve for impaired accounts	603	373
Amount of the general component of the allowance	1,962	3,652
Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired receivables specifically evaluated	129	109
Finance receivables evaluated collectively	30,373	32,941
Finance receivables	30,502	33,050	$ 31,286
Impaired receivables in nonaccrual status	53	28
Amount of the specific reserve for impaired accounts	62	20
Amount of the general component of the allowance	$ 2,305	$ 2,568

The amount of allowance for credit losses excluding the specific reserve associated with impaired accounts.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

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- Definition

Amount of allowance for credit losses related to recorded investment.

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-Publisher FASB
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-SubTopic 10
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- Definition

Reflects the carrying amount of loans deemed to be questionable as to collection on which no interest is continuing to be recognized.

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-Publisher FASB
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- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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