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Allowance for Credit Losses - Recorded Investment in Commercial Loan Classes by Internally Assigned Risk Ratings (Details) - USD ($) $ in Thousands | Sep. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance | $ 7,394,868 | $ 7,137,152
Commercial |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance | 5,810,034 | $ 5,512,796
Total percentage of recorded investment in commercial loan |  | 100.00%
Commercial | Pass |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 5,254,056
Total percentage of recorded investment in commercial loan |  | 95.30%
Commercial | Special mention |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 103,878
Total percentage of recorded investment in commercial loan |  | 1.90%
Commercial | Substandard |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 152,651
Total percentage of recorded investment in commercial loan |  | 2.80%
Commercial | Doubtful |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 2,211
Total percentage of recorded investment in commercial loan |  | 0.00%
Commercial | Commercial real estate |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance | 3,290,138 | $ 3,416,518
Total percentage of recorded investment in commercial loan |  | 100.00%
Commercial | Commercial real estate | Pass |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 3,270,438
Total percentage of recorded investment in commercial loan |  | 95.70%
Commercial | Commercial real estate | Special mention |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 57,285
Total percentage of recorded investment in commercial loan |  | 1.70%
Commercial | Commercial real estate | Substandard |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 86,772
Total percentage of recorded investment in commercial loan |  | 2.50%
Commercial | Commercial real estate | Doubtful |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 2,023
Total percentage of recorded investment in commercial loan |  | 0.10%
Commercial | Commercial and industrial |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance | 2,042,467 | $ 1,720,833
Total percentage of recorded investment in commercial loan |  | 100.00%
Commercial | Commercial and industrial | Pass |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 1,636,314
Total percentage of recorded investment in commercial loan |  | 95.10%
Commercial | Commercial and industrial | Special mention |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 36,484
Total percentage of recorded investment in commercial loan |  | 2.10%
Commercial | Commercial and industrial | Substandard |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 47,980
Total percentage of recorded investment in commercial loan |  | 2.80%
Commercial | Commercial and industrial | Doubtful |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 55
Total percentage of recorded investment in commercial loan |  | 0.00%
Commercial | Commercial construction |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance | $ 477,429 | $ 375,445
Total percentage of recorded investment in commercial loan |  | 100.00%
Commercial | Commercial construction | Pass |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 347,304
Total percentage of recorded investment in commercial loan |  | 92.50%
Commercial | Commercial construction | Special mention |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 10,109
Total percentage of recorded investment in commercial loan |  | 2.70%
Commercial | Commercial construction | Substandard |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 17,899
Total percentage of recorded investment in commercial loan |  | 4.80%
Commercial | Commercial construction | Doubtful |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 133
Total percentage of recorded investment in commercial loan |  | 0.00%

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