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Qualified Affordable Housing (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) commitment	Dec. 31, 2016 USD ($) commitment	Dec. 31, 2015 USD ($)
Schedule of Equity Method Investments [Line Items]
Investments in qualified affordable housing projects	$ 9,000,000	$ 11,700,000
Number of open commitments to fund future investments in qualified affordable housing | commitment	1	0
Open commitments to fund future investments qualified affordable housing projects	$ 800,000	$ 0
Tax credits to offset amortization expense of investments in affordable housing projects	3,400,000	3,700,000	$ 4,000,000
Noninterest Expense
Schedule of Equity Method Investments [Line Items]
Amortization expense of investments in qualified affordable housing projects	$ 3,000,000	$ 3,300,000	$ 3,600,000

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Qualified Affordable Housing Project Investments, Commitment, Number

+ References

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Amount of affordable housing tax credits and other tax benefits recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=64813897&loc=SL49122993-202985

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64813897&loc=SL49122993-202985

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=64813897&loc=SL49122993-202985

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-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=64813897&loc=SL49122993-202985

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