Summary of Significant Accounting Policies (Impact of Adoption of New Accounting Standard Related to CECL) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss	$ 160		$ 0
Financing Receivable, Allowance for Credit Loss	263,177		132,167
Off-Balance Sheet, Credit Loss, Liability	44,152		500		$ 500		$ 428
Cumulative effect of accounting change			(29,252)		(14,672)		(2,285)
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)	$ (2,300)	(2,285)
Commercial Portfolio Segment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	73,843		51,593		48,580		59,614
Commercial Portfolio Segment [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change		(16,798)
Commercial and Industrial Total Energy Loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	39,553		37,382		29,052		51,528
Commercial and Industrial Total Energy Loans [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change		8,258
Commercial Real Estate Portfolio Segment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	134,892		31,037		38,777		30,948
Commercial Real Estate Portfolio Segment [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change		10,680
Total consumer real estate loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	7,926		4,113		6,103		5,657
Total consumer real estate loans [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change		(1,890)
Consumer Loan [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	6,963		8,042		9,620		7,617
Consumer Loan [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change		1,776
Loans Receivable [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss	263,177		132,167		$ 132,132		$ 155,364
Loans Receivable [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change		2,026
US Treasury [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change		0
Residential Mortgage Backed Securities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss	0		0
Residential Mortgage Backed Securities [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change		0
States and Political Subdivisions [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss	160		0
States and Political Subdivisions [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change		(170)
Other [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss	0		0
Other [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change		0
Debt Securities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss	$ 160		$ 0
Debt Securities [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change		(170)
Commitments to Extend Credit [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change		(31,108)
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 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt 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]
Debt Securities, Held-to-maturity, Allowance for Credit Loss		0
Pre-Adoption Allowance [Member] | States and Political Subdivisions [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss		0
Pre-Adoption Allowance [Member] | Other [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt 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]
Debt 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
Accounting Standards Update 2016-13 [Member] | Commercial Portfolio Segment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		21,263
Accounting Standards Update 2016-13 [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)
Accounting Standards Update 2016-13 [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)
Accounting Standards Update 2016-13 [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
Accounting Standards Update 2016-13 [Member] | Consumer Loan [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		(2,248)
Accounting Standards Update 2016-13 [Member] | Loans Receivable [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Financing Receivable, Allowance for Credit Loss		(2,565)
Accounting Standards Update 2016-13 [Member] | US Treasury [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss		0
Accounting Standards Update 2016-13 [Member] | Residential Mortgage Backed Securities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss		0
Accounting Standards Update 2016-13 [Member] | States and Political Subdivisions [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss		215
Accounting Standards Update 2016-13 [Member] | Other [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss		0
Accounting Standards Update 2016-13 [Member] | Debt Securities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss		215
Accounting Standards Update 2016-13 [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 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt 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]
Debt Securities, Held-to-maturity, Allowance for Credit Loss		0
Post-Adoption Allowance [Member] | States and Political Subdivisions [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss		215
Post-Adoption Allowance [Member] | Other [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Debt 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]
Debt 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