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Loans and Loans Held for Sale - Additional Information (Details) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2019 USD ($) loan | Mar. 31, 2018 loan | Dec. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loans, net of unearned income | $ 4,700 |  | $ 5,300
Threshold period of satisfactory performance for troubled debt restructuring to be restored to accruing status | 6 months |  |
Number of troubled debt restructuring loans returned to accruing status | loan | 3 | 0 |
Amount of trouble debt restructuring loans returned to accruing status | $ 1,700 |  |
Number of commitments to lend additional funds on TDRs | loan | 14 |  |
Commitments to lend additional funds on TDRs | $ 13,000 |  |
Minimum period of loan payment defaults following restructure for TDRs to be in default | 90 days |  |
Number of defaulted TDRs that were restructured within the last twelve months prior to defaulting | loan | 0 | 0 |
Commercial |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Percentage of commercial loans in total portfolio loans | 79.00% |  | 79.00%
Commercial loans | $ 4,660,290 |  | $ 4,672,445
Commercial real estate and commercial construction | Commercial |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Commercial loans | $ 3,100,000 |  | $ 3,200,000
Combined percentage of commercial real estate and commercial construction in total commercial loans | 68.00% |  | 68.00%
Combined percentage of commercial real estate and commercial construction in total portfolio loans | 53.00% |  | 53.00%
Concentration risk percentage of commercial real estate and commercial construction | 0.00% |  | 0.00%
Maximum concentration of commercial real estate and commercial construction portfolio in loans (in excess of) | 13.20% |  | 14.00%
Out of market exposure of combined portfolio (percent) | 5.70% |  | 5.40%
Percentage of total loans out-of-state excluding contiguous states | 3.00% |  | 2.90%

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