Finance Receivables, Credit Quality Information, and Allowance for Credit Losses - Summary of Finance Receivables Evaluated for Impairment (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired receivables specifically evaluated	$ 11,411	$ 7,260
Finance receivables evaluated collectively	706,364	621,184
Finance receivables	717,775	628,444	$ 546,192
Impaired receivables in nonaccrual status	1,080	719
Amount of the specific reserve for impaired accounts	2,374	1,708
Amount of the general component of the allowance	38,876	35,744
Small Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired receivables specifically evaluated	2,409	1,009
Finance receivables evaluated collectively	356,062	337,148
Finance receivables	358,471	338,157	319,533
Impaired receivables in nonaccrual status	288	204
Amount of the specific reserve for impaired accounts	563	266
Amount of the general component of the allowance	21,207	21,269
Large Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired receivables specifically evaluated	6,441	2,760
Finance receivables evaluated collectively	228,908	143,793
Finance receivables	235,349	146,553	46,147
Impaired receivables in nonaccrual status	610	83
Amount of the specific reserve for impaired accounts	1,216	560
Amount of the general component of the allowance	10,244	5,033
Automobile Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired receivables specifically evaluated	2,460	3,370
Finance receivables evaluated collectively	87,972	112,739
Finance receivables	90,432	116,109	154,382
Impaired receivables in nonaccrual status	175	415
Amount of the specific reserve for impaired accounts	576	862
Amount of the general component of the allowance	5,334	7,966
Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired receivables specifically evaluated	101	121
Finance receivables evaluated collectively	33,422	27,504
Finance receivables	33,523	27,625	$ 26,130
Impaired receivables in nonaccrual status	7	17
Amount of the specific reserve for impaired accounts	19	20
Amount of the general component of the allowance	$ 2,091	$ 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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-Section 50
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-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5074-111524

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