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Loans and Loans Held for Sale - Narrative (Details) $ in Thousands | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2021 USD ($) SecurityLoan | Mar. 31, 2021 USD ($) | Sep. 30, 2020 USD ($) SecurityLoan | Sep. 30, 2021 USD ($) SecurityLoan | Sep. 30, 2020 USD ($) SecurityLoan | Dec. 31, 2020 USD ($) SecurityLoan
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Unearned income | $ 14,500 |  |  | $ 14,500 |  | $ 16,000
Purchase accounting fair value adjustments | 6,400 |  |  | 6,400 |  | 8,600
Total loans | 6,861,739 |  |  | 6,861,739 |  | 7,108,248
Loans held for investment, outstanding balance | $ 6,970,087 |  |  | $ 6,970,087 |  | 7,225,860
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 | SecurityLoan | 1 |  | 2 | 6 | 3 |
Financing receivable, troubled debt restructuring, returned to accruing status | $ 100 |  | $ 100 | $ 500 | $ 22,700 |
Number of commitments to lend additional funds on TDRs | SecurityLoan | 12 |  |  | 12 |  |
Commitments to lend additional funds on TDRs | $ 300 |  |  | $ 300 |  |
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 | SecurityLoan | 0 |  | 0 | 0 | 6 |
Amount of defaulted TDRs that were restructured within the last twelve months prior to defaulting |  |  |  |  | $ 18,100 |
Commercial |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans held for investment, outstanding balance | $ 5,423,964 |  |  | $ 5,423,964 |  | $ 5,673,707
Financing receivable, before allowance for credit loss, reclassification during period |  | $ 90,200 |  |  |  |
Percentage of commercial loans in total portfolio loans | 77.80% |  |  | 77.80% |  | 78.50%
Commercial | CARES Act, Paycheck Protection Program Loans |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Total loans | $ 181,000 |  |  | $ 181,000 |  | $ 465,000
Number of modified loans | SecurityLoan |  |  |  | 42 |  | 52
Modified loans |  |  |  | $ 58,900 |  | $ 195,600
Business banking portfolio |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans held for investment, outstanding balance | 1,100,000 |  |  | 1,100,000 |  | 1,200,000
Business banking portfolio | CARES Act, Paycheck Protection Program Loans |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Decrease in finance receivables | (100,500) |  |  | (100,500) |  |
Consumer |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans held for investment, outstanding balance | 1,546,123 |  |  | 1,546,123 |  | 1,552,153
Financing receivable, before allowance for credit loss, reclassification during period |  | $ 23,200 |  |  |  |
Commercial real estate | Commercial |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans held for investment, outstanding balance | 2,702,780 |  |  | 2,702,780 |  | 2,791,947
Commercial real estate | Business banking portfolio |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans held for investment, outstanding balance | 523,100 |  |  | 523,100 |  | 453,000
Commercial and industrial | Commercial |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans held for investment, outstanding balance | 1,478,198 |  |  | 1,478,198 |  | 1,559,552
Commercial and industrial | Business banking portfolio |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans held for investment, outstanding balance | 220,600 |  |  | 220,600 |  | 394,900
Commercial and industrial | Business banking portfolio | CARES Act, Paycheck Protection Program Loans |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans held for investment, outstanding balance | 78,000 |  |  | 78,000 |  | 178,400
Commercial construction | Commercial |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans held for investment, outstanding balance | 485,924 |  |  | 485,924 |  | 466,077
Commercial construction | Business banking portfolio |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans held for investment, outstanding balance | 13,400 |  |  | 13,400 |  | 8,200
Consumer real estate | Business banking portfolio |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans held for investment, outstanding balance | 343,000 |  |  | 343,000 |  |
Consumer real estate | Consumer |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans held for investment, outstanding balance | 1,105,478 |  |  | 1,105,478 |  | 1,167,332
Business banking | Commercial |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans held for investment, outstanding balance | 1,100,125 |  |  | 1,100,125 |  | 1,160,067
Business banking | Consumer |  |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |
Loans held for investment, outstanding balance |  |  |  |  |  | 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
Combined percentage of commercial real estate and commercial construction in total commercial loans | 68.70% |  |  | 68.70% |  | 65.60%
Combined percentage of commercial real estate and commercial construction in total portfolio loans | 53.40% |  |  | 53.40% |  | 51.50%
Out of market exposure of combined portfolio | 5.00% |  |  | 5.00% |  | 5.90%
Percentage of total loans out-of-state excluding contiguous states | 2.70% |  |  | 2.70% |  | 3.00%

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