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)