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Allowance for Loan Losses - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans considered nonperforming (in days)			90 days
Threshold for evaluation for impairment of substandard and nonaccrual commercial loans	$ 500,000.0		$ 500,000.0
Change-off arising from participation loan agreement	8,632,000	$ 5,822,000	10,076,000	$ 8,763,000
Other consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Change-off arising from participation loan agreement	414,000	$ 370,000	872,000	$ 804,000
Other consumer | Vehicles and Equipment Liens
Financing Receivable, Allowance for Credit Losses [Line Items]
Change-off arising from participation loan agreement	5,200,000		5,200,000
Participating loans, total exposure	4,900,000		4,900,000
Participating loans, direct exposure	$ 950,000		$ 950,000

X

- Definition

Minimum amount over which evaluation for impairment of substandard and nonaccrual commercial loans are made.

+ References

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- Definition

Participating Loans, Direct Exposure

+ References

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- Definition

Participating Loans, Total Exposure

+ References

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- Definition

Period interest and principal of loan due treated as loans considered nonperforming.

+ References

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- Definition

Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ 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 (c)(3)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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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

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