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Investment Securities - Amortized Cost of Investment Securities Held to Maturity (Details) - USD ($) $ in Thousands | Jun. 30, 2021 | Dec. 31, 2020
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Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | $ 1,721,659 | $ 1,227,668
Aaa |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 115,430 |
Aa1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 131,246 |
Aa2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 136,008 |
Aa3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 96,915 |
A1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 66,549 |
A2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 18,962 |
A3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 1,065 |
Baa2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 527 |
Non-rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 1,154,957 |
State and municipal |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 863,426 | $ 619,927
State and municipal | Aaa |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 54,753 |
State and municipal | Aa1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 131,246 |
State and municipal | Aa2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 136,008 |
State and municipal | Aa3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 96,915 |
State and municipal | A1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 66,549 |
State and municipal | A2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 18,962 |
State and municipal | A3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 1,065 |
State and municipal | Baa2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 527 |
State and municipal | Non-rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 357,401 |
Other |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 858,233 |
Other | Aaa |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 60,677 |
Other | Aa1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 0 |
Other | Aa2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 0 |
Other | Aa3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 0 |
Other | A1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 0 |
Other | A2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 0 |
Other | A3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 0 |
Other | Baa2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | 0 |
Other | Non-rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized cost of investment securities held to maturity | $ 797,556 |

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- Definition Amount excluding accrued interest, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919230-210447 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 3B -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446 + Details
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