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Allowance for Credit Losses - Recorded Investment in Commercial Loan Classes by Internally Assigned Risk Ratings (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance | $ 7,225,860 | $ 7,137,152
Commercial |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance | $ 5,977,643 | $ 5,756,971
Total percentage of recorded investment in commercial loan |  | 100.00%
Commercial | Pass |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Total percentage of recorded investment in commercial loan |  | 95.30%
Commercial | Special mention |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Total percentage of recorded investment in commercial loan |  | 1.90%
Commercial | Substandard |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Total percentage of recorded investment in commercial loan |  | 2.80%
Commercial | Doubtful |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
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 |  | $ 3,416,518
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 |  | $ 3,270,437
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 |  | $ 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 |  | $ 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 |  | $ 347,324
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%
Commercial | Total |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 5,512,796
Commercial | Total | Pass |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | 5,254,056
Commercial | Total | Special mention |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | 103,878
Commercial | Total | Substandard |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | 152,651
Commercial | Total | Doubtful |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Loans held for investment, outstanding balance |  | $ 2,211

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