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Loans and Loans Held for Sale - Additional Information (Details) $ in Thousands |  |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Mar. 31, 2021 USD ($) loan | Dec. 31, 2020 USD ($) | Mar. 31, 2021 USD ($) loan | Mar. 31, 2020 USD ($) loan | Dec. 31, 2020 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Unearned income | $ 14,000 | $ 16,000 | $ 14,000 |  | $ 16,000
Purchase accounting fair value adjustments | 7,500 | 8,600 |  |  |
Total loans | 7,068,067 | 7,108,248 | 7,068,067 |  | 7,108,248
Loans held for investment, outstanding balance | $ 7,183,168 | 7,225,860 | $ 7,183,168 |  | 7,225,860
Threshold period of satisfactory performance for troubled debt restructuring to be restored to accruing status |  |  | 6 months |  |
Restructured loans |  |  | $ 6,865 | $ 1,897 |
Number of troubled debt restructuring loans returned to accruing status | loan |  |  | 0 | 0 |
Number of commitments to lend additional funds on TDRs | loan | 20 |  | 20 |  |
Commitments to lend additional funds on TDRs | $ 800 |  | $ 800 |  |
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 |  |  |  | 11 |
Amount of defaulted TDRs that were restructured within the last twelve months prior to defaulting |  |  |  | $ 21,100 |
Commercial |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Loans held for investment, outstanding balance | $ 5,676,683 | $ 5,673,707 | $ 5,676,683 |  | $ 5,673,707
Financing receivable, before allowance for credit loss, reclassification during period |  |  | $ 90,200 |  |
Percentage of commercial loans in total portfolio loans | 79.00% | 78.50% | 79.00% |  | 78.50%
Commercial | CARES Act, Paycheck Protection Program Loans |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Restructured loans |  |  | $ 61,800 |  |
Number of modified loans | loan |  |  | 40 |  | 52
Modified loans |  |  | $ 61,800 |  | $ 195,600
Business banking portfolio |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Loans held for investment, outstanding balance | $ 1,100,000 | $ 1,200,000 | 1,100,000 |  | 1,200,000
Consumer |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Loans held for investment, outstanding balance | 1,506,485 | 1,552,153 | 1,506,485 |  | 1,552,153
Financing receivable, before allowance for credit loss, reclassification during period |  |  | 23,200 |  |
CARES Act, Paycheck Protection Program Loans | Commercial |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Total loans | 499,100 |  | 499,100 |  |
Commercial real estate | Commercial |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Loans held for investment, outstanding balance | 2,780,327 | 2,791,947 | 2,780,327 |  | 2,791,947
Restructured loans |  |  | 0 | 0 |
Commercial real estate | Business banking portfolio |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Loans held for investment, outstanding balance | 504,200 | 453,000 | 504,200 |  | 453,000
Commercial and industrial | Commercial |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Loans held for investment, outstanding balance | 1,699,588 | 1,559,552 | 1,699,588 |  | 1,559,552
Restructured loans |  |  | 6,296 | 0 |
Commercial and industrial | Business banking portfolio |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Loans held for investment, outstanding balance | 232,100 | 394,900 | 232,100 |  | 394,900
Commercial construction | Commercial |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Loans held for investment, outstanding balance | 449,459 | 466,077 | 449,459 |  | 466,077
Restructured loans |  |  | 0 | 1,806 |
Commercial construction | Business banking portfolio |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Loans held for investment, outstanding balance | 11,000 | 8,200 | 11,000 |  | 8,200
Business banking | Commercial |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Loans held for investment, outstanding balance | 1,069,078 | 1,160,067 | 1,069,078 |  | 1,160,067
Restructured loans |  |  | 0 | $ 0 |
Business banking | Consumer |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Loans held for investment, outstanding balance | 321,800 | 303,900 | 321,800 |  | 303,900
CRE and commercial construction | Commercial |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Loans held for investment, outstanding balance | $ 3,700,000 | $ 3,700,000 | $ 3,700,000 |  | $ 3,700,000
Combined percentage of commercial real estate and commercial construction in total commercial loans | 66.00% | 65.60% | 66.00% |  | 65.60%
Combined percentage of commercial real estate and commercial construction in total portfolio loans | 52.10% | 51.50% | 52.10% |  | 51.50%
Out of market exposure of combined portfolio (percent) | 5.70% | 5.90% | 5.70% |  | 5.90%
Percentage of total loans out-of-state excluding contiguous states | 3.00% | 3.00% | 3.00% |  | 3.00%
Nonperforming TDRs |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Financing receivable, nonperforming assets, period increase (decrease) |  |  | $ 11,600 |  |
Nonperforming TDRs | Commercial real estate | Commercial |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Restructured loans |  |  | 4,600 |  |
Nonperforming TDRs | Commercial and industrial | Commercial |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Restructured loans |  |  | 11,100 |  |
Amount charged down |  |  | $ 3,900 |  |

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