Loans (Non-Accrual Loans, Segregated by Class of Loan and Year of Origination) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Non-accrual loans	$ 61,449	$ 102,303
Commercial Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	1,397,141
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	608,464
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	343,825
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	258,737
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	121,652
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	119,250
Financing Receivable, Revolving	2,019,121
Non-accrual loans	19,849	26,038
Commercial and Industrial Total Energy Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	524,270
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	48,853
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	16,310
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	8,083
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	2,174
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	5,346
Financing Receivable, Revolving	592,094
Non-accrual loans	23,168	65,761
Paycheck Protection Program [Member]
Loans and Leases Receivable Disclosure [Line Items]
Non-accrual loans	0	0
Commercial Real Estate, Buildings, Land and Other [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	1,629,815
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,086,073
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	883,701
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	764,197
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	495,617
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	804,894
Financing Receivable, Revolving	74,403
Non-accrual loans	15,737	8,912
Construction Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	420,477
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	452,644
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	196,170
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	2,915
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	1,144
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	1,758
Financing Receivable, Revolving	147,575
Non-accrual loans	1,684	665
Total consumer real estate loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Non-accrual loans	993	922
Consumer Loan [Member]
Loans and Leases Receivable Disclosure [Line Items]
Non-accrual loans	18	$ 5
Nonperforming Financial Instruments [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	16,498
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	15,154
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	4,989
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	3,719
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	2,038
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	3,532
Financing Receivable, Revolving	12,414
Financing Receivable, Revolving, Converted to Term Loan	3,105
Nonperforming Financial Instruments [Member] | Commercial Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	9,479
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	3,351
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	1,846
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	1,489
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	105
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	29
Financing Receivable, Revolving	839
Financing Receivable, Revolving, Converted to Term Loan	2,711
Nonperforming Financial Instruments [Member] | Commercial and Industrial Total Energy Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	2,421
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	6,772
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	2,144
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	0
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	359
Financing Receivable, Revolving	11,193
Financing Receivable, Revolving, Converted to Term Loan	279
Nonperforming Financial Instruments [Member] | Paycheck Protection Program [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	0
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	0
Financing Receivable, Revolving	0
Financing Receivable, Revolving, Converted to Term Loan	0
Nonperforming Financial Instruments [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	2,914
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	5,031
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	999
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	2,019
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	1,933
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	2,736
Financing Receivable, Revolving	105
Financing Receivable, Revolving, Converted to Term Loan	0
Nonperforming Financial Instruments [Member] | Construction Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	1,684
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	0
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	0
Financing Receivable, Revolving	0
Financing Receivable, Revolving, Converted to Term Loan	0
Nonperforming Financial Instruments [Member] | Total consumer real estate loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	211
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	408
Financing Receivable, Revolving	259
Financing Receivable, Revolving, Converted to Term Loan	115
Nonperforming Financial Instruments [Member] | Consumer Loan [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	0
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	0
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	0
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	0
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	0
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	0
Financing Receivable, Revolving	18
Financing Receivable, Revolving, Converted to Term Loan	$ 0