Allowance for Credit Losses (Recorded Investments in Troubled Debt Restructured Loans) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Pre-modification outstanding recorded investment	$ 1,934	$ 1,934
Post-modification outstanding recorded investment	2,065	2,065
Recorded Investment	1,841	1,857
Residential Mortgage [Member]
Pre-modification outstanding recorded investment	754	754
Post-modification outstanding recorded investment	883	883
Recorded Investment	681	690
Commercial Mortgage [Member]
Pre-modification outstanding recorded investment	992	992
Post-modification outstanding recorded investment	992	992
Recorded Investment	977	982
Consumer: Home Equity [Member]
Pre-modification outstanding recorded investment	148	148
Post-modification outstanding recorded investment	148	148
Recorded Investment	144	146
Consumer: Other [Member]
Pre-modification outstanding recorded investment	40	40
Post-modification outstanding recorded investment	42	42
Recorded Investment	$ 39	$ 39

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

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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- Definition

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

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- Definition

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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