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Allowance for Loan Losses - Investments in Loans Considered to be Impaired and Related Information on Impaired Loans (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Financing Receivable, Impaired [Line Items] |  |
With a related allowance recorded, Recorded Investment | $ 1,783 | $ 991
With a related allowance recorded, Unpaid Principal Balance | 1,835 | 2,460
Without a related allowance recorded, Recorded Investment | 25,040 | 40,944
Without a related allowance, Unpaid Principal Balance | 31,302 | 48,539
Impaired financing receivables | 26,823 | 41,935
Impaired Financing Receivable, Unpaid Principal Balance, Total | 33,137 | 50,999
Impaired Financing Receivable, Related Allowance, Total | 77 | 798
With a related allowance recorded, Average Recorded Investment | 1,025 | 2,468
With a related allowance recorded, Interest Income Recognized | 56 | 2
Without a related allowance recorded, Average Recorded Investment | 34,421 | 43,334
Without a related allowance recorded, Interest Income Recognized | 1,174 | 990
Impaired Financing Receivable, Average Recorded Investment, Total | 35,446 | 45,802
Impaired Financing Receivable, Interest Income Recognized, Total | 1,230 | 992
Commercial real estate |  |
Financing Receivable, Impaired [Line Items] |  |
With a related allowance recorded, Recorded Investment | 0 | 0
With a related allowance recorded, Unpaid Principal Balance | 0 | 0
Without a related allowance recorded, Recorded Investment | 3,546 | 16,352
Without a related allowance, Unpaid Principal Balance | 3,811 | 17,654
Impaired financing receivables | 3,546 | 16,352
Impaired Financing Receivable, Unpaid Principal Balance, Total | 3,811 | 17,654
Impaired Financing Receivable, Related Allowance, Total | 0 | 0
With a related allowance recorded, Average Recorded Investment | 0 | 0
With a related allowance recorded, Interest Income Recognized | 0 | 0
Without a related allowance recorded, Average Recorded Investment | 6,636 | 17,496
Without a related allowance recorded, Interest Income Recognized | 177 | 144
Impaired Financing Receivable, Average Recorded Investment, Total | 6,636 | 17,496
Impaired Financing Receivable, Interest Income Recognized, Total | 177 | 144
Commercial and industrial |  |
Financing Receivable, Impaired [Line Items] |  |
With a related allowance recorded, Recorded Investment | 1,735 | 964
With a related allowance recorded, Unpaid Principal Balance | 1,787 | 2,433
Without a related allowance recorded, Recorded Investment | 5,549 | 5,902
Without a related allowance, Unpaid Principal Balance | 7,980 | 7,699
Impaired financing receivables | 7,284 | 6,866
Impaired Financing Receivable, Unpaid Principal Balance, Total | 9,767 | 10,132
Impaired Financing Receivable, Related Allowance, Total | 29 | 771
With a related allowance recorded, Average Recorded Investment | 968 | 2,438
With a related allowance recorded, Interest Income Recognized | 52 | 0
Without a related allowance recorded, Average Recorded Investment | 9,897 | 6,141
Without a related allowance recorded, Interest Income Recognized | 257 | 160
Impaired Financing Receivable, Average Recorded Investment, Total | 10,865 | 8,579
Impaired Financing Receivable, Interest Income Recognized, Total | 309 | 160
Commercial construction |  |
Financing Receivable, Impaired [Line Items] |  |
With a related allowance recorded, Recorded Investment | 0 | 0
With a related allowance recorded, Unpaid Principal Balance | 0 | 0
Without a related allowance recorded, Recorded Investment | 5,464 | 6,613
Without a related allowance, Unpaid Principal Balance | 8,132 | 10,306
Impaired financing receivables | 5,464 | 6,613
Impaired Financing Receivable, Unpaid Principal Balance, Total | 8,132 | 10,306
Impaired Financing Receivable, Related Allowance, Total | 0 | 0
With a related allowance recorded, Average Recorded Investment | 0 | 0
With a related allowance recorded, Interest Income Recognized | 0 | 0
Without a related allowance recorded, Average Recorded Investment | 6,828 | 7,723
Without a related allowance recorded, Interest Income Recognized | 253 | 162
Impaired Financing Receivable, Average Recorded Investment, Total | 6,828 | 7,723
Impaired Financing Receivable, Interest Income Recognized, Total | 253 | 162
Consumer real estate |  |
Financing Receivable, Impaired [Line Items] |  |
With a related allowance recorded, Recorded Investment | 21 | 26
With a related allowance recorded, Unpaid Principal Balance | 21 | 26
Without a related allowance recorded, Recorded Investment | 10,467 | 12,053
Without a related allowance, Unpaid Principal Balance | 11,357 | 12,849
Impaired financing receivables | 10,488 | 12,079
Impaired Financing Receivable, Unpaid Principal Balance, Total | 11,378 | 12,875
Impaired Financing Receivable, Related Allowance, Total | 21 | 26
With a related allowance recorded, Average Recorded Investment | 23 | 28
With a related allowance recorded, Interest Income Recognized | 2 | 2
Without a related allowance recorded, Average Recorded Investment | 11,037 | 11,939
Without a related allowance recorded, Interest Income Recognized | 487 | 523
Impaired Financing Receivable, Average Recorded Investment, Total | 11,060 | 11,967
Impaired Financing Receivable, Interest Income Recognized, Total | 489 | 525
Other consumer |  |
Financing Receivable, Impaired [Line Items] |  |
With a related allowance recorded, Recorded Investment | 27 | 1
With a related allowance recorded, Unpaid Principal Balance | 27 | 1
Without a related allowance recorded, Recorded Investment | 14 | 24
Without a related allowance, Unpaid Principal Balance | 22 | 31
Impaired financing receivables | 41 | 25
Impaired Financing Receivable, Unpaid Principal Balance, Total | 49 | 32
Impaired Financing Receivable, Related Allowance, Total | 27 | 1
With a related allowance recorded, Average Recorded Investment | 34 | 2
With a related allowance recorded, Interest Income Recognized | 2 | 0
Without a related allowance recorded, Average Recorded Investment | 23 | 35
Without a related allowance recorded, Interest Income Recognized | 0 | 1
Impaired Financing Receivable, Average Recorded Investment, Total | 57 | 37
Impaired Financing Receivable, Interest Income Recognized, Total | $ 2 | $ 1

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