Finance Receivables, Credit Quality Information, and Allowance for Credit Losses - Summary of Finance Receivables Evaluated for Impairment (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired receivables specifically evaluated	$ 10,047	$ 7,260
Finance receivables evaluated collectively	686,102	621,184
Finance receivables	696,149	628,444	$ 601,608
Impaired receivables in nonaccrual status	745	719
Amount of the specific reserve for impaired accounts	2,095	1,708
Amount of the general component of the allowance	37,005	35,744
Small Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired receivables specifically evaluated	2,084	1,009
Finance receivables evaluated collectively	347,306	337,148
Finance receivables	349,390	338,157	328,207
Impaired receivables in nonaccrual status	231	204
Amount of the specific reserve for impaired accounts	487	266
Amount of the general component of the allowance	20,313	21,269
Large Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired receivables specifically evaluated	5,322	2,760
Finance receivables evaluated collectively	211,780	143,793
Finance receivables	217,102	146,553	119,731
Impaired receivables in nonaccrual status	314	83
Amount of the specific reserve for impaired accounts	972	560
Amount of the general component of the allowance	8,828	5,033
Automobile Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired receivables specifically evaluated	2,526	3,370
Finance receivables evaluated collectively	94,615	112,739
Finance receivables	97,141	116,109	128,131
Impaired receivables in nonaccrual status	191	415
Amount of the specific reserve for impaired accounts	615	862
Amount of the general component of the allowance	5,885	7,966
Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired receivables specifically evaluated	115	121
Finance receivables evaluated collectively	32,401	27,504
Finance receivables	32,516	27,625	$ 25,539
Impaired receivables in nonaccrual status	9	17
Amount of the specific reserve for impaired accounts	21	20
Amount of the general component of the allowance	$ 1,979	$ 1,476

Financing receivables in bankruptcy that are on nonaccrual status as of the balance sheet date.

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- Definition

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

+ References

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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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

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- Definition

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

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- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 15
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-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522

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-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5074-111524

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