Loans and Allowances for Credit Losses, Troubled Debt Restructurings (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	$ 168,739	$ 129,485	$ 168,739	$ 129,485	$ 147,117
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	70,906	60,646	70,906	60,646	74,738
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	97,833	68,839	97,833	68,839	72,379
Troubled Debt Restructuring, Specific allowance	4,308	64	4,308	64	46
Troubled Debt Restructuring, Charge-offs	10	600	42	744
Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	88,115	50,679	88,115	50,679	65,747
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	46,400	32,647	46,400	32,647	47,449
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	41,715	18,032	41,715	18,032	18,298
Troubled Debt Restructuring, Specific allowance	4,308	64	4,308	64	46
Troubled Debt Restructuring, Charge-offs	10	600	42	744
Nonaccrual [Member] | Commercial
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	60,924	14,732	60,924	14,732	36,879
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	30,007	11,236	30,007	11,236	29,225
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	30,917	3,496	30,917	3,496	7,654
Troubled Debt Restructuring, Specific allowance	4,308	0	4,308	0	0
Troubled Debt Restructuring, Charge-offs	3	500	3	557
Nonaccrual [Member] | Commercial | Energy [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	22,466	2,246	22,466	2,246	16,893
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	12,692	0	12,692	0	10,867
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	9,774	2,246	9,774	2,246	6,026
Troubled Debt Restructuring, Specific allowance	4,308	0	4,308	0	0
Troubled Debt Restructuring, Charge-offs	0	500	0	500
Nonaccrual [Member] | Commercial | Services [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	7,208	8,610	7,208	8,610	7,527
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	6,561	7,853	6,561	7,853	6,830
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	647	757	647	757	697
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	3	0	3	0
Nonaccrual [Member] | Commercial | Wholesale/retail [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	10,524	2,467	10,524	2,467	11,291
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	10,524	2,427	10,524	2,427	11,251
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	40	0	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	195	253	195	253	224
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	195	253	195	253	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	640	0	640	607
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	0	640	0	640	0
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	0	0	0	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	20,531	516	20,531	516	337
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	35	63	35	63	53
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	20,496	453	20,496	453	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	1,168	3,810	1,168	3,810	1,707
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	811	2,510	811	2,510	1,114
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	357	1,300	357	1,300	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	381	1,601	381	1,601	690
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	145	1,079	145	1,079	97
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	236	522	236	522	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	301	1,264	301	1,264	326
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	301	907	301	907	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	121	152	121	152	143
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	0	152	0	152	143
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	121	0	121	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	365	793	365	793	548
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	365	372	365	372	548
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	421	0	421	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	25,795	31,839	25,795	31,839	26,924
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	15,354	18,625	15,354	18,625	16,874
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	10,441	13,214	10,441	13,214	10,050
Troubled Debt Restructuring, Specific allowance	0	64	0	64	46
Troubled Debt Restructuring, Charge-offs	0	97	31	178
Nonaccrual [Member] | Residential mortgage | Permanent mortgage [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	14,284	17,367	14,284	17,367	14,876
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	9,939	12,462	9,939	12,462	10,175
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	4,345	4,905	4,345	4,905	4,701
Troubled Debt Restructuring, Specific allowance	0	64	0	64	46
Troubled Debt Restructuring, Charge-offs	0	37	0	52
Nonaccrual [Member] | Residential mortgage | Permanent mortgages guaranteed by US government agencies [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	5,962	9,709	5,962	9,709	6,702
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	1,176	2,024	1,176	2,024	2,241
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	4,786	7,685	4,786	7,685	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	5,549	4,763	5,549	4,763	5,346
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	4,239	4,139	4,239	4,139	4,458
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	1,310	624	1,310	624	888
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	60	31	126
Nonaccrual [Member] | Personal
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	228	298	228	298	237
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	228	276	228	276	236
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	22	0	22	1
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	7	3	8	9
Accruing [Member] | Residential mortgage | Permanent mortgages guaranteed by US government agencies [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	80,624	78,806	80,624	78,806	81,370
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	24,506	27,999	24,506	27,999	27,289
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	56,118	50,807	56,118	50,807	54,081
Troubled Debt Restructuring, Specific allowance	0	0	0	0	$ 0
Troubled Debt Restructuring, Charge-offs	$ 0	$ 0	$ 0	$ 0