Significant Accounting Policies Significant Accounting Policies - Impact of Adoption of New Accounting Standard Related to CECL (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Securities, held-to-maturity, allowance for credit loss	$ 160			$ 0
Financing Receivable, Allowance for Credit Loss	263,475			132,167
Off-Balance Sheet, Credit Loss, Liability	43,663	$ 46,939		500	$ 500	$ 500		$ 500
Cumulative effect of accounting change				(29,252)				(14,672)
Commercial Portfolio Segment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	72,505	98,536		51,593	52,667	57,714		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	54,631	40,817		37,382	33,346	25,818		29,052
Commercial Real Estate Portfolio Segment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	118,593	93,425		31,037	35,353	35,914		38,777
Total consumer real estate loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	10,277	8,998		4,113	4,884	5,637		6,103
Consumer Loan [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	7,469	8,285		8,042	10,309	9,846		9,620
Loans Receivable [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	263,475	250,061		132,167	$ 136,559	$ 134,929		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	160			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	$ 160	$ 172		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]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change			(29,300)	$ (29,252)			$ (14,700)	$ (14,672)
Retained Earnings [Member] | Commercial Portfolio Segment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change			(16,798)
Retained Earnings [Member] | Commercial and Industrial Total Energy Loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change			8,258
Retained Earnings [Member] | Commercial Real Estate Portfolio Segment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change			10,680
Retained Earnings [Member] | Total consumer real estate loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change			(1,890)
Retained Earnings [Member] | Consumer Loan [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change			1,776
Retained Earnings [Member] | Loans Receivable [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change			2,026
Retained Earnings [Member] | US Treasury Securities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change			0
Retained Earnings [Member] | Residential Mortgage Backed Securities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change			0
Retained Earnings [Member] | US States and Political Subdivisions Debt Securities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change			(170)
Retained Earnings [Member] | Other Investments [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change			0
Retained Earnings [Member] | Debt Securities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change			(170)
Retained Earnings [Member] | Commitments to Extend Credit [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change			$ (31,108)