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Allowance for Credit Losses - Summary of Allowance for Credit Losses and Recorded Investments (Details) - USD ($) $ in Thousands | Sep. 30, 2020 | Jun. 30, 2020 | Jan. 01, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Dec. 31, 2018
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Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |
Allowance for Loan Losses, Individually Evaluated for Impairment |  |  |  | $ 2,200 |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment |  |  |  | 60,024 |  |  |
Total | $ 120,998 | $ 114,609 | $ 62,224 | 62,224 | $ 62,115 | $ 61,479 | $ 60,996
Portfolio Loans, Individually Evaluated for Impairment |  |  |  | 75,337 |  |  |
Portfolio Loans, Collectively Evaluated for Impairment |  |  |  | 7,061,815 |  |  |
Total | 7,394,868 |  |  | 7,137,152 |  |  |
Commercial |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |
Total | 5,810,034 |  |  | 5,512,796 |  |  |
Consumer |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |
Total | 1,584,834 |  |  | 1,624,356 |  |  |
Commercial real estate | Commercial |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |
Allowance for Loan Losses, Individually Evaluated for Impairment |  |  |  | 2,023 |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment |  |  |  | 28,554 |  |  |
Total |  |  |  | 30,577 |  |  |
Portfolio Loans, Individually Evaluated for Impairment |  |  |  | 47,920 |  |  |
Portfolio Loans, Collectively Evaluated for Impairment |  |  |  | 3,368,598 |  |  |
Total | 3,290,138 |  |  | 3,416,518 |  |  |
Commercial and industrial | Commercial |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |
Allowance for Loan Losses, Individually Evaluated for Impairment |  |  |  | 55 |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment |  |  |  | 15,626 |  |  |
Total |  |  |  | 15,681 |  |  |
Portfolio Loans, Individually Evaluated for Impairment |  |  |  | 17,606 |  |  |
Portfolio Loans, Collectively Evaluated for Impairment |  |  |  | 1,703,227 |  |  |
Total | 2,042,467 |  |  | 1,720,833 |  |  |
Commercial construction | Commercial |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |
Allowance for Loan Losses, Individually Evaluated for Impairment |  |  |  | 113 |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment |  |  |  | 7,787 |  |  |
Total |  |  |  | 7,900 |  |  |
Portfolio Loans, Individually Evaluated for Impairment |  |  |  | 1,914 |  |  |
Portfolio Loans, Collectively Evaluated for Impairment |  |  |  | 373,531 |  |  |
Total | $ 477,429 |  |  | 375,445 |  |  |
Consumer real estate | Consumer |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |
Allowance for Loan Losses, Individually Evaluated for Impairment |  |  |  | 0 |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment |  |  |  | 6,337 |  |  |
Total |  |  |  | 6,337 |  |  |
Portfolio Loans, Individually Evaluated for Impairment |  |  |  | 7,884 |  |  |
Portfolio Loans, Collectively Evaluated for Impairment |  |  |  | 1,537,439 |  |  |
Total |  |  |  | 1,545,323 |  |  |
Other consumer | Consumer |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |  |  |
Allowance for Loan Losses, Individually Evaluated for Impairment |  |  |  | 9 |  |  |
Allowance for Loan Losses, Collectively Evaluated for Impairment |  |  |  | 1,720 |  |  |
Total |  |  |  | 1,729 |  |  |
Portfolio Loans, Individually Evaluated for Impairment |  |  |  | 13 |  |  |
Portfolio Loans, Collectively Evaluated for Impairment |  |  |  | 79,020 |  |  |
Total |  |  |  | $ 79,033 |  |  |

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