Derivative Financial Instruments - Fair Value Hedges (Details) - Interest rate swaps - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net gains and losses recognized in income related to derivatives in fair value hedging relationships
Net losses recognized on fair value hedges	$ (639)	$ (1,436)	$ (2,402)
Minimum \| Fair value hedges
Fair hedges carried
Fixed interest rate (as a percent)	2.59%
Maximum \| Fair value hedges
Fair hedges carried
Fixed interest rate (as a percent)	3.44%
Net interest income \| Fair value hedges
Net gains and losses recognized in income related to derivatives in fair value hedging relationships
Expense recorded	$ (644)	(1,226)	(2,472)
Noninterest income
Net gains and losses recognized in income related to derivatives in fair value hedging relationships
Gains (losses) recognized on derivatives	846	956	1,803
Gains (losses) recognized on hedged item	(841)	(1,166)	(1,733)
Net gains (losses) recognized on fair value hedges (ineffective portion)	5	(210)	$ 70
Derivatives designated as hedging instruments
Fair hedges carried
Notional amounts	194,687	200,504
Derivatives designated as hedging instruments \| Fair value hedges
Fair hedges carried
Notional amounts	44,700	50,500
Positive fair value	0	0
Fair value losses	$ 500	$ 1,500

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986

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- Definition

Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

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- Definition

The premium (cost) of a hedge, net of any cash received on settlement during the period.

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- Definition

Fixed interest rate related to the interest rate derivative.

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Amount of gain (loss)recognized in the income statement from the hedging ineffectiveness of a fair value hedge.

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- Definition

Total amount of gain (loss) derived from fair value hedges recognized in earnings in the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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- Definition

Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611

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Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities.

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