Allowance for Credit Losses (Narrative) (Details) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018 USD ($) loan	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) loan
Financing Receivable, Modifications [Line Items]
Number of TDR loans \| loan	8		8
TDR recorded investment	$ 1,841		$ 1,857
Partial charge-off of loan amount	$ 76	$ 349
Number of defaulted TDRs \| loan	0		0
Loan defaults on TDRs	$ 0	$ 0
Accruing Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of TDR loans \| loan	5		5
TDR recorded investment	$ 1,121		$ 1,128
Nonaccrual Impaired Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of TDR loans \| loan	3		3
TDR recorded investment	$ 720		$ 729
Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Real estate loans in process of foreclosure	$ 869		$ 638
Number of TDR loans \| loan	2		2
Partial charge-off of loan amount	$ 151		$ 151
Consumer Installment Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of TDR loans \| loan	1		1
Partial charge-off of loan amount	$ 2		$ 2
Other Real Estate Owned [Member]
Financing Receivable, Modifications [Line Items]
Real estate loans in process of foreclosure	$ 74		$ 149
Commercial Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Number of TDR loans \| loan			3
TDR recorded investment			$ 992

Amount of direct write-downs of financing receivables charged against the allowance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

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Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

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The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=82895541&loc=d3e18845-111554

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Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953682-111524

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Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

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Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
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-Section 50
-Paragraph 35
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