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Investment Securities - Amortized Cost of Investment Securities Held to Maturity (Details) - USD ($) $ in Thousands | Mar. 31, 2022 | Dec. 31, 2021
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Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | $ 2,325,311 | $ 2,180,047
Aaa |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 156,735 |
Aa1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 152,330 |
Aa2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 174,021 |
Aa3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 130,579 |
A1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 105,264 |
A2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 30,114 |
A3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 10,110 |
Non-rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 1,566,158 |
State and municipal |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 1,082,257 | $ 1,057,301
State and municipal | Aaa |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 96,155 |
State and municipal | Aa1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 152,330 |
State and municipal | Aa2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 174,021 |
State and municipal | Aa3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 130,579 |
State and municipal | A1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 105,264 |
State and municipal | A2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 30,114 |
State and municipal | A3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 10,110 |
State and municipal | Non-rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 383,684 |
Other |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 1,243,054 |
Other | Aaa |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 60,580 |
Other | Aa1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 0 |
Other | Aa2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 0 |
Other | Aa3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 0 |
Other | A1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 0 |
Other | A2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 0 |
Other | A3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | 0 |
Other | Non-rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Amortized Cost | $ 1,182,474 |

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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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