Loans and Allowances for Credit Losses, Troubled Debt Restructurings (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	$ 128,986	$ 126,126	$ 128,986	$ 126,126	$ 147,117
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	60,479	59,919	60,479	59,919	74,738
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	68,507	66,207	68,507	66,207	72,379
Troubled Debt Restructuring, Specific allowance	0	62	0	62	46
Troubled Debt Restructuring, Charge-offs	4,370	543	4,412	1,230
Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	59,546	45,820	59,546	45,820	65,747
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	45,531	30,899	45,531	30,899	47,449
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	14,015	14,921	14,015	14,921	18,298
Troubled Debt Restructuring, Specific allowance	0	62	0	62	46
Troubled Debt Restructuring, Charge-offs	4,370	543	4,412	1,230
Nonaccrual [Member] | Commercial
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	32,381	13,192	32,381	13,192	36,879
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	29,679	9,620	29,679	9,620	29,225
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	2,702	3,572	2,702	3,572	7,654
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	4,329	500	4,332	1,057
Nonaccrual [Member] | Commercial | Energy [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	9,582	1,746	9,582	1,746	16,893
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	9,506	0	9,506	0	10,867
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	76	1,746	76	1,746	6,026
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	4,322	500	4,322	1,000
Nonaccrual [Member] | Commercial | Services [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	720	7,761	720	7,761	7,527
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	103	7,034	103	7,034	6,830
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	617	727	617	727	697
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	7	0	10	0
Nonaccrual [Member] | Commercial | Wholesale/retail [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	1,802	2,327	1,802	2,327	11,291
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	0	2,287	0	2,287	11,251
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	1,802	40	1,802	40	40
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Nonaccrual [Member] | Commercial | Manufacturing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	180	238	180	238	224
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	180	238	180	238	224
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	0	0	0	0
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Nonaccrual [Member] | Commercial | Healthcare [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	0	623	0	623	607
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	0	0	0	0	0
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	623	0	623	607
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Nonaccrual [Member] | Commercial | Other commercial and industrial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	20,097	497	20,097	497	337
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	19,890	61	19,890	61	53
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	207	436	207	436	284
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0	0	57
Nonaccrual [Member] | Commercial real estate
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	969	2,858	969	2,858	1,707
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	733	2,066	733	2,066	1,114
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	236	792	236	792	593
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Nonaccrual [Member] | Commercial real estate | Residential construction and land development [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	327	794	327	794	690
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	91	359	91	359	97
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	236	435	236	435	593
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Nonaccrual [Member] | Commercial real estate | Retail [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	289	1,249	289	1,249	326
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	289	892	289	892	326
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	357	0	357	0
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Nonaccrual [Member] | Commercial real estate | Office [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	0	149	0	149	143
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	0	149	0	149	143
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	0	0	0	0
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Nonaccrual [Member] | Commercial real estate | Multifamily [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	0	0	0	0	0
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	0	0	0	0	0
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	0	0	0	0
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Nonaccrual [Member] | Commercial real estate | Industrial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	0	0	0	0	0
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	0	0	0	0	0
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	0	0	0	0
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Nonaccrual [Member] | Commercial real estate | Other commercial real estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	353	666	353	666	548
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	353	666	353	666	548
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	0	0	0	0
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Nonaccrual [Member] | Residential mortgage
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	25,991	29,497	25,991	29,497	26,924
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	14,924	18,942	14,924	18,942	16,874
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	11,067	10,555	11,067	10,555	10,050
Troubled Debt Restructuring, Specific allowance	0	62	0	62	46
Troubled Debt Restructuring, Charge-offs	39	34	70	155
Nonaccrual [Member] | Residential mortgage | Permanent mortgage [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	14,765	16,109	14,765	16,109	14,876
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	10,188	11,944	10,188	11,944	10,175
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	4,577	4,165	4,577	4,165	4,701
Troubled Debt Restructuring, Specific allowance	0	62	0	62	46
Troubled Debt Restructuring, Charge-offs	0	0	0	2
Nonaccrual [Member] | Residential mortgage | Permanent mortgages guaranteed by US government agencies [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	5,601	8,220	5,601	8,220	6,702
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	523	2,331	523	2,331	2,241
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	5,078	5,889	5,078	5,889	4,461
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Nonaccrual [Member] | Residential mortgage | Home equity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	5,625	5,168	5,625	5,168	5,346
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	4,213	4,667	4,213	4,667	4,458
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	1,412	501	1,412	501	888
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	39	34	70	153
Nonaccrual [Member] | Personal
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	205	273	205	273	237
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	195	271	195	271	236
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	10	2	10	2	1
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	2	9	10	18
Accruing [Member] | Residential mortgage | Permanent mortgages guaranteed by US government agencies [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	69,440	80,306	69,440	80,306	81,370
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	14,948	29,020	14,948	29,020	27,289
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	54,492	51,286	54,492	51,286	54,081
Troubled Debt Restructuring, Specific allowance	0	0	0	0	$ 0
Troubled Debt Restructuring, Charge-offs	$ 0	$ 0	$ 0	$ 0