Loans and Allowances for Credit Losses, Nonaccrual (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	$ 234,693	$ 180,951
Financing Receivable, Nonaccrual, No Allowance	167,878
Financing receivable, Nonaccrual, With Allowance	66,815
Financing Receivable, Nonaccrual, Related Allowance	22,441
Commercial [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	167,159	115,416
Financing Receivable, Nonaccrual, No Allowance	113,945
Financing receivable, Nonaccrual, With Allowance	53,214
Financing Receivable, Nonaccrual, Related Allowance	19,052
Commercial [Member] | Energy [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	125,059	91,722
Financing Receivable, Nonaccrual, No Allowance	76,633
Financing receivable, Nonaccrual, With Allowance	48,426
Financing Receivable, Nonaccrual, Related Allowance	16,478
Commercial [Member] | Healthcare [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	3,645	4,480
Financing Receivable, Nonaccrual, No Allowance	3,645
Financing receivable, Nonaccrual, With Allowance	0
Financing Receivable, Nonaccrual, Related Allowance	0
Commercial [Member] | Services [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	25,598	7,483
Financing Receivable, Nonaccrual, No Allowance	20,810
Financing receivable, Nonaccrual, With Allowance	4,788
Financing Receivable, Nonaccrual, Related Allowance	2,574
Commercial [Member] | General business [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	12,857
Financing Receivable, Nonaccrual, No Allowance	12,857
Financing receivable, Nonaccrual, With Allowance	0
Financing Receivable, Nonaccrual, Related Allowance	0
Commercial real estate [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	27,246	27,626
Financing Receivable, Nonaccrual, No Allowance	13,645
Financing receivable, Nonaccrual, With Allowance	13,601
Financing Receivable, Nonaccrual, Related Allowance	3,389
Loans to individuals [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	40,288
Financing Receivable, Nonaccrual, No Allowance	40,288
Financing receivable, Nonaccrual, With Allowance	0
Financing Receivable, Nonaccrual, Related Allowance	0
Loans to individuals [Member] | Residential mortgage [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	32,228
Financing Receivable, Nonaccrual, No Allowance	32,228
Financing receivable, Nonaccrual, With Allowance	0
Financing Receivable, Nonaccrual, Related Allowance	0
Loans to individuals [Member] | Personal [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	319	$ 287
Financing Receivable, Nonaccrual, No Allowance	319
Financing receivable, Nonaccrual, With Allowance	0
Financing Receivable, Nonaccrual, Related Allowance	0
US Government Agency Insured Loans | Loans to individuals [Member] | Residential mortgage [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	7,741
Financing Receivable, Nonaccrual, No Allowance	7,741
Financing receivable, Nonaccrual, With Allowance	0
Financing Receivable, Nonaccrual, Related Allowance	$ 0