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Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Summary of Significant Accounting Policies [Abstract] |  |  |
Minimum number of days past due for nonaccrual loan status | 90 days |  |
Period of sustained repayment performance for nonperforming TDRs to be returned to performing status | 6 months |  |
Standby letters of credit expiration period | 1 year |  |
Noninterest Income [Abstract] |  |  |
Total noninterest income in-scope of ASC 606 | $ 134,455 | $ 126,012 | $ 113,444
Total noninterest income out-of-scope of ASC 606 | 9,568 | (1,250) | 7,860
Total noninterest income | 144,023 | 124,762 | 121,304
Insurance and Other Financial Services Revenue [Member] |  |  |
Noninterest Income [Abstract] |  |  |
Total noninterest income in-scope of ASC 606 | 25,006 | 24,345 | 23,532
Service Charges on Deposit Accounts [Member] |  |  |
Noninterest Income [Abstract] |  |  |
Total noninterest income in-scope of ASC 606 | 17,151 | 17,224 | 16,750
ATM and Debit Card Fees [Member] |  |  |
Noninterest Income [Abstract] |  |  |
Total noninterest income in-scope of ASC 606 | 23,893 | 22,699 | 21,372
Retirement Plan Administration Fees [Member] |  |  |
Noninterest Income [Abstract] |  |  |
Total noninterest income in-scope of ASC 606 | 30,388 | 26,992 | 20,213
Trust [Member] |  |  |
Noninterest Income [Abstract] |  |  |
Total noninterest income in-scope of ASC 606 | 19,164 | 19,524 | 19,586
Other [Member] |  |  |
Noninterest Income [Abstract] |  |  |
Total noninterest income in-scope of ASC 606 | $ 18,853 | $ 15,228 | $ 11,991

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- Definition Period of sustained repayment performance for nonperforming TDRs to be returned to performing status, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Definition Represents expiration period of standby letters of credit, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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