Loans and Allowances for Credit Losses, Troubled Debt Restructurings (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	$ 159,541	$ 129,035	$ 147,117
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	86,852	58,676	74,738
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	72,689	70,359	72,379
Troubled Debt Restructuring, Specific allowance	316	75	46
Troubled Debt Restructuring, Charge-offs	21	133
Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	75,964	51,437	65,747
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	57,812	30,261	47,449
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	18,152	21,176	18,298
Troubled Debt Restructuring, Specific allowance	316	75	46
Troubled Debt Restructuring, Charge-offs	21	133
Nonaccrual [Member] | Commercial
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	47,993	15,782	36,879
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	40,799	11,631	29,225
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	7,194	4,151	7,654
Troubled Debt Restructuring, Specific allowance	271	9	0
Troubled Debt Restructuring, Charge-offs	0	57
Nonaccrual [Member] | Commercial | Energy [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	28,529	2,829	16,893
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	22,883	0	10,867
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	5,646	2,829	6,026
Troubled Debt Restructuring, Specific allowance	271	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial | Services [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	7,356	8,863	7,527
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	6,679	8,076	6,830
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	677	787	697
Troubled Debt Restructuring, Specific allowance	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial | Wholesale/retail [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	10,984	2,619	11,291
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	10,984	2,567	11,251
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	52	40
Troubled Debt Restructuring, Specific allowance	0	9	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial | Manufacturing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	209	267	224
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	209	267	224
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	0	0
Troubled Debt Restructuring, Specific allowance	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial | Healthcare [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	601	656	607
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	0	656	0
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	601	0	607
Troubled Debt Restructuring, Specific allowance	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial | Other commercial and industrial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	314	548	337
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	44	65	53
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	270	483	284
Troubled Debt Restructuring, Specific allowance	0	0	0
Troubled Debt Restructuring, Charge-offs	0	57
Nonaccrual [Member] | Commercial real estate
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	1,459	4,242	1,707
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	1,101	1,859	1,114
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	358	2,383	593
Troubled Debt Restructuring, Specific allowance	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial real estate | Residential construction and land development [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	630	1,871	690
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	272	296	97
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	358	1,575	593
Troubled Debt Restructuring, Specific allowance	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial real estate | Retail [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	314	1,302	326
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	314	925	326
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	377	0
Troubled Debt Restructuring, Specific allowance	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial real estate | Office [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	138	160	143
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	138	160	143
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	0	0
Troubled Debt Restructuring, Specific allowance	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial real estate | Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	0	0	0
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	0	0	0
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	0	0
Troubled Debt Restructuring, Specific allowance	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial real estate | Industrial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	0	0	0
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	0	0	0
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	0	0
Troubled Debt Restructuring, Specific allowance	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial real estate | Other commercial real estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	377	909	548
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	377	478	548
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	431	0
Troubled Debt Restructuring, Specific allowance	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Residential mortgage
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	26,309	31,129	26,924
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	15,709	16,509	16,874
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	10,600	14,620	10,050
Troubled Debt Restructuring, Specific allowance	45	66	46
Troubled Debt Restructuring, Charge-offs	20	69
Nonaccrual [Member] | Residential mortgage | Permanent mortgage [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	14,457	16,242	14,876
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	9,876	11,451	10,175
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	4,581	4,791	4,701
Troubled Debt Restructuring, Specific allowance	45	66	46
Troubled Debt Restructuring, Charge-offs	0	3
Nonaccrual [Member] | Residential mortgage | Permanent mortgages guaranteed by US government agencies [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	6,189	9,809	6,702
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	1,597	851	2,241
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	4,592	8,958	4,461
Troubled Debt Restructuring, Specific allowance	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Residential mortgage | Home equity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	5,663	5,078	5,346
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	4,236	4,207	4,458
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	1,427	871	888
Troubled Debt Restructuring, Specific allowance	0	0	0
Troubled Debt Restructuring, Charge-offs	20	66
Nonaccrual [Member] | Personal
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	203	284	237
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	203	262	236
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	22	1
Troubled Debt Restructuring, Specific allowance	0	0	0
Troubled Debt Restructuring, Charge-offs	1	7
Accruing [Member] | Residential mortgage | Permanent mortgages guaranteed by US government agencies [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	83,577	77,598	81,370
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	29,040	28,415	27,289
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	54,537	49,183	54,081
Troubled Debt Restructuring, Specific allowance	0	0	$ 0
Troubled Debt Restructuring, Charge-offs	$ 0	$ 0