Loans and Allowances for Credit Losses, Troubled Debt Restructurings (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	$ 124,176	$ 119,871	$ 124,176	$ 119,871	$ 114,350
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	52,142	48,994	52,142	48,994	41,719
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	72,034	70,877	72,034	70,877	72,631
Troubled Debt Restructuring, Specific allowance	254	3,293	254	3,293	285
Troubled Debt Restructuring, Charge-offs	250	159	312	305
Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	42,578	49,412	42,578	49,412	40,365
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	29,790	25,996	29,790	25,996	24,445
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	12,788	23,416	12,788	23,416	15,920
Troubled Debt Restructuring, Specific allowance	254	3,293	254	3,293	285
Troubled Debt Restructuring, Charge-offs	250	159	312	305
Commercial [Member] | Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	13,834	9,258	13,834	9,258	6,061
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	12,407	4,567	12,407	4,567	4,423
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	1,427	4,691	1,427	4,691	1,638
Troubled Debt Restructuring, Specific allowance	157	3,157	157	3,157	157
Troubled Debt Restructuring, Charge-offs	100	0	100	0
Commercial [Member] | Energy [Member] | Nonaccrual [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
Commercial [Member] | Services [Member] | Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	9,362	1,714	9,362	1,714	1,666
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	8,502	724	8,502	724	706
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	860	990	860	990	960
Troubled Debt Restructuring, Specific allowance	148	148	148	148	148
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Commercial [Member] | Wholesale/retail [Member] | Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	2,897	3,545	2,897	3,545	3,381
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	2,844	3,440	2,844	3,440	3,284
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	53	105	53	105	97
Troubled Debt Restructuring, Specific allowance	9	9	9	9	9
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Commercial [Member] | Manufacturing [Member] | Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	296	3,355	296	3,355	340
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	296	355	296	355	340
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	3,000	0	3,000	0
Troubled Debt Restructuring, Specific allowance	0	3,000	0	3,000	0
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Commercial [Member] | Healthcare [Member] | Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	689	0	689	0	0
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	689	0	689	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
Commercial [Member] | Other commercial and industrial [Member] | Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	590	644	590	644	674
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	76	48	76	48	93
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	514	596	514	596	581
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	100	0	100	0
Commercial Real Estate [Member] | Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	5,101	16,314	5,101	16,314	10,711
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	3,337	5,687	3,337	5,687	4,720
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	1,764	10,627	1,764	10,627	5,991
Troubled Debt Restructuring, Specific allowance	0	56	0	56	23
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Commercial Real Estate [Member] | Residential construction and land development [Member] | Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	2,539	8,562	2,539	8,562	3,140
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	1,624	264	1,624	264	641
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	915	8,298	915	8,298	2,499
Troubled Debt Restructuring, Specific allowance	0	56	0	56	23
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Commercial Real Estate [Member] | Retail [Member] | Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	1,356	3,664	1,356	3,664	3,600
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	960	2,486	960	2,486	2,432
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	396	1,178	396	1,178	1,168
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Commercial Real Estate [Member] | Office [Member] | Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	169	2,345	169	2,345	2,324
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	169	1,194	169	1,194	0
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	1,151	0	1,151	2,324
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Commercial Real Estate [Member] | Multifamily [Member] | Nonaccrual [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
Commercial Real Estate [Member] | Industrial [Member] | Nonaccrual [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
Commercial Real Estate [Member] | Other commercial real estate [Member] | Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	1,037	1,743	1,037	1,743	1,647
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	584	1,743	584	1,743	1,647
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	453	0	453	0	0
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Residential Mortgage [Member] | Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	23,278	23,366	23,278	23,366	23,174
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	13,837	15,420	13,837	15,420	15,049
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	9,441	7,946	9,441	7,946	8,125
Troubled Debt Restructuring, Specific allowance	97	80	97	80	105
Troubled Debt Restructuring, Charge-offs	150	159	210	304
Residential Mortgage [Member] | Permanent mortgage [Member] | Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	16,359	16,764	16,359	16,764	16,393
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	9,361	11,227	9,361	11,227	11,134
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	6,998	5,537	6,998	5,537	5,259
Troubled Debt Restructuring, Specific allowance	97	80	97	80	105
Troubled Debt Restructuring, Charge-offs	140	147	142	246
Residential Mortgage [Member] | Permanent mortgages guaranteed by US government agencies [Member] | Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	1,944	1,665	1,944	1,665	1,597
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	140	329	140	329	179
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	1,804	1,336	1,804	1,336	1,418
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0		0	0
Residential Mortgage [Member] | Permanent mortgages guaranteed by US government agencies [Member] | Accruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	81,598	70,459	81,598	70,459	73,985
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	22,352	22,998	22,352	22,998	17,274
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	59,246	47,461	59,246	47,461	56,711
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	0	0	0	0
Residential Mortgage [Member] | Home equity {Member] | Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	4,975	4,937	4,975	4,937	5,184
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	4,336	3,864	4,336	3,864	3,736
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	639	1,073	639	1,073	1,448
Troubled Debt Restructuring, Specific allowance	0	0	0	0	0
Troubled Debt Restructuring, Charge-offs	10	12	68	58
Personal [Member] | Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	365	474	365	474	419
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	209	322	209	322	253
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	156	152	156	152	166
Troubled Debt Restructuring, Specific allowance	0	0	0	0	$ 0
Troubled Debt Restructuring, Charge-offs	$ 0	$ 0	$ 2	$ 1