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Investment Securities - Non-Marketable Securities (Details)	9 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares	Oct. 26, 2017	Dec. 31, 2016 USD ($)
Schedule of Cost-method Investments [Line Items]
Federal Home Loan Bank stock, par value (usd per share) | $ / shares	$ 100
Investments in low income housing tax credit funds	$ 2,300,000		$ 2,500,000
Low income housing tax credits and other tax benefits	249,000
Low income housing amortization expense	199,000
Unfunded commitments for low income housing tax credit funds	$ 549,000
Visa Inc. | Visa Inc. Class B common stock
Schedule of Cost-method Investments [Line Items]
Conversion rate on common stock	1.6483
Visa Inc. Class B common stock
Schedule of Cost-method Investments [Line Items]
Number of shares of securities carried at cost | shares	16,939
Carrying value of securities carried at cost	$ 0
Fair value of Class B common stock	2,900,000		2,200,000
Subsequent event
Schedule of Cost-method Investments [Line Items]
Federal Home Loan Bank, dividend rate percentage		7.00%
Other assets
Schedule of Cost-method Investments [Line Items]
Federal Home Loan Bank stock	$ 10,200,000		$ 10,200,000

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