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Significant Accounting Policies Significant Accounting Policies - Impact of Adoption of New Accounting Standard Related to CECL (Details) - USD ($) $ in Thousands | Jan. 01, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | --- | --- | --- | --- | --- | ---
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss |  | $ 172 |  | $ 0 |  |  |
Financing Receivable, Allowance for Credit Loss |  | 250,061 |  | 132,167 |  |  |
Off-Balance Sheet, Credit Loss, Liability |  | 46,939 | $ 42,164 | 500 | $ 500 | $ 500 | $ 500
Cumulative Effect on Retained Earnings, Net of Tax | $ (29,300) |  |  |  |  |  |
Commercial Portfolio Segment [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss |  | 98,536 | 92,152 | 51,593 | 57,714 | 58,571 | 48,580
Commercial and Industrial Total Energy Loans [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss |  | 40,817 | 103,201 | 37,382 | 25,818 | 25,343 | 29,052
Commercial Real Estate Portfolio Segment [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss |  | 93,425 | 52,319 | 31,037 | 35,914 | 36,455 | 38,777
Total consumer real estate loans [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss |  | 8,998 | 8,170 | 4,113 | 5,637 | 5,661 | 6,103
Consumer Loan [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss |  | 8,285 | 8,039 | 8,042 | 9,846 | 10,320 | 9,620
Loans Receivable [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss |  | 250,061 | 263,881 | 132,167 | $ 134,929 | $ 136,350 | $ 132,132
Residential Mortgage Backed Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss |  | 0 |  | 0 |  |  |
US States and Political Subdivisions Debt Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss |  | 172 |  | 0 |  |  |
Other Investments [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss |  | 0 |  | 0 |  |  |
Debt Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss |  | $ 172 | $ 200 | $ 0 |  |  |
Pre-Adoption Allowance [Member] | Commercial Portfolio Segment [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | 51,593 |  |  |  |  |  |
Pre-Adoption Allowance [Member] | Commercial and Industrial Total Energy Loans [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | 37,382 |  |  |  |  |  |
Pre-Adoption Allowance [Member] | Commercial Real Estate Portfolio Segment [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | 31,037 |  |  |  |  |  |
Pre-Adoption Allowance [Member] | Total consumer real estate loans [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | 4,113 |  |  |  |  |  |
Pre-Adoption Allowance [Member] | Consumer Loan [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | 8,042 |  |  |  |  |  |
Pre-Adoption Allowance [Member] | Loans Receivable [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | 132,167 |  |  |  |  |  |
Pre-Adoption Allowance [Member] | US Treasury Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss | 0 |  |  |  |  |  |
Pre-Adoption Allowance [Member] | Residential Mortgage Backed Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss | 0 |  |  |  |  |  |
Pre-Adoption Allowance [Member] | US States and Political Subdivisions Debt Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss | 0 |  |  |  |  |  |
Pre-Adoption Allowance [Member] | Other Investments [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss | 0 |  |  |  |  |  |
Pre-Adoption Allowance [Member] | Debt Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss | 0 |  |  |  |  |  |
Pre-Adoption Allowance [Member] | Commitments to Extend Credit [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Off-Balance Sheet, Credit Loss, Liability | 500 |  |  |  |  |  |
Impact of Adoption [Member] | Commercial Portfolio Segment [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | 21,263 |  |  |  |  |  |
Impact of Adoption [Member] | Commercial and Industrial Total Energy Loans [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | (10,453) |  |  |  |  |  |
Impact of Adoption [Member] | Commercial Real Estate Portfolio Segment [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | (13,519) |  |  |  |  |  |
Impact of Adoption [Member] | Total consumer real estate loans [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | 2,392 |  |  |  |  |  |
Impact of Adoption [Member] | Consumer Loan [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | (2,248) |  |  |  |  |  |
Impact of Adoption [Member] | Loans Receivable [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | (2,565) |  |  |  |  |  |
Impact of Adoption [Member] | US Treasury Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss | 0 |  |  |  |  |  |
Impact of Adoption [Member] | Residential Mortgage Backed Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss | 0 |  |  |  |  |  |
Impact of Adoption [Member] | US States and Political Subdivisions Debt Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss | 215 |  |  |  |  |  |
Impact of Adoption [Member] | Other Investments [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss | 0 |  |  |  |  |  |
Impact of Adoption [Member] | Debt Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss | 215 |  |  |  |  |  |
Impact of Adoption [Member] | Commitments to Extend Credit [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Off-Balance Sheet, Credit Loss, Liability | 39,377 |  |  |  |  |  |
Post-Adoption Allowance [Member] | Commercial Portfolio Segment [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | 72,856 |  |  |  |  |  |
Post-Adoption Allowance [Member] | Commercial and Industrial Total Energy Loans [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | 26,929 |  |  |  |  |  |
Post-Adoption Allowance [Member] | Commercial Real Estate Portfolio Segment [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | 17,518 |  |  |  |  |  |
Post-Adoption Allowance [Member] | Total consumer real estate loans [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | 6,505 |  |  |  |  |  |
Post-Adoption Allowance [Member] | Consumer Loan [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | 5,794 |  |  |  |  |  |
Post-Adoption Allowance [Member] | Loans Receivable [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Financing Receivable, Allowance for Credit Loss | 129,602 |  |  |  |  |  |
Post-Adoption Allowance [Member] | US Treasury Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss | 0 |  |  |  |  |  |
Post-Adoption Allowance [Member] | Residential Mortgage Backed Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss | 0 |  |  |  |  |  |
Post-Adoption Allowance [Member] | US States and Political Subdivisions Debt Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss | 215 |  |  |  |  |  |
Post-Adoption Allowance [Member] | Other Investments [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss | 0 |  |  |  |  |  |
Post-Adoption Allowance [Member] | Debt Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Securities, held-to-maturity, allowance for credit loss | 215 |  |  |  |  |  |
Post-Adoption Allowance [Member] | Commitments to Extend Credit [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Off-Balance Sheet, Credit Loss, Liability | 39,877 |  |  |  |  |  |
Retained Earnings [Member] | Commercial Portfolio Segment [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Cumulative Effect on Retained Earnings, Net of Tax | (16,798) |  |  |  |  |  |
Retained Earnings [Member] | Commercial and Industrial Total Energy Loans [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Cumulative Effect on Retained Earnings, Net of Tax | 8,258 |  |  |  |  |  |
Retained Earnings [Member] | Commercial Real Estate Portfolio Segment [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Cumulative Effect on Retained Earnings, Net of Tax | 10,680 |  |  |  |  |  |
Retained Earnings [Member] | Total consumer real estate loans [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Cumulative Effect on Retained Earnings, Net of Tax | (1,890) |  |  |  |  |  |
Retained Earnings [Member] | Consumer Loan [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Cumulative Effect on Retained Earnings, Net of Tax | 1,776 |  |  |  |  |  |
Retained Earnings [Member] | Loans Receivable [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Cumulative Effect on Retained Earnings, Net of Tax | 2,026 |  |  |  |  |  |
Retained Earnings [Member] | US Treasury Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Cumulative Effect on Retained Earnings, Net of Tax | 0 |  |  |  |  |  |
Retained Earnings [Member] | Residential Mortgage Backed Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Cumulative Effect on Retained Earnings, Net of Tax | 0 |  |  |  |  |  |
Retained Earnings [Member] | US States and Political Subdivisions Debt Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Cumulative Effect on Retained Earnings, Net of Tax | (170) |  |  |  |  |  |
Retained Earnings [Member] | Other Investments [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Cumulative Effect on Retained Earnings, Net of Tax | 0 |  |  |  |  |  |
Retained Earnings [Member] | Debt Securities [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Cumulative Effect on Retained Earnings, Net of Tax | (170) |  |  |  |  |  |
Retained Earnings [Member] | Commitments to Extend Credit [Member] |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |
Cumulative Effect on Retained Earnings, Net of Tax | $ (31,108) |  |  |  |  |  |

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