Loans and Allowances for Credit Losses, Troubled Debt Restructurings (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	$ 114,350	$ 106,281
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	41,719	42,343
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	72,631	63,938
Troubled Debt Restructuring, Specific allowance	285	441
Troubled Debt Restructuring, Charge-offs	5,107	1,481
Accruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	73,985	54,322
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	17,274	13,384
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	56,711	40,938
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	40,365	51,959
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	24,445	28,959
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	15,920	23,000
Troubled Debt Restructuring, Specific allowance	285	441
Troubled Debt Restructuring, Charge-offs	5,107	1,481
Commercial [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	6,061	3,632
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	4,423	1,114
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	1,638	2,518
Troubled Debt Restructuring, Specific allowance	157	246
Troubled Debt Restructuring, Charge-offs	3,000	154
Energy [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	0	0
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	0	0
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	0
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Services [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	1,666	2,235
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	706	852
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	960	1,383
Troubled Debt Restructuring, Specific allowance	148	237
Troubled Debt Restructuring, Charge-offs	0	0
Wholesale/retail [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	3,381	235
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	3,284	89
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	97	146
Troubled Debt Restructuring, Specific allowance	9	9
Troubled Debt Restructuring, Charge-offs	0	0
Manufacturing [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	340	391
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	340	0
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	391
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	3,000	154
Healthcare [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	0	0
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	0	0
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	0
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Other commercial and industrial [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	674	771
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	93	173
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	581	598
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Commercial Real Estate [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	10,711	24,577
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	4,720	11,342
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	5,991	13,235
Troubled Debt Restructuring, Specific allowance	23	107
Troubled Debt Restructuring, Charge-offs	1,597	745
Residential construction and land development [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	3,140	10,148
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	641	1,444
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	2,499	8,704
Troubled Debt Restructuring, Specific allowance	23	107
Troubled Debt Restructuring, Charge-offs	1,597	46
Retail [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	3,600	4,359
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	2,432	3,141
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	1,168	1,218
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	582
Office [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	2,324	5,059
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	0	3,872
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	2,324	1,187
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	117
Multifamily [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	0	0
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	0	0
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	0
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Industrial [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	0	0
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	0	0
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	0
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Other commercial real estate [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	1,647	5,011
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	1,647	2,885
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	2,126
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Residential Mortgage [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	23,174	22,742
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	15,049	15,745
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	8,125	6,997
Troubled Debt Restructuring, Specific allowance	105	88
Troubled Debt Restructuring, Charge-offs	509	581
Permanent mortgage [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	16,393	18,697
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	11,134	12,214
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	5,259	6,483
Troubled Debt Restructuring, Specific allowance	105	88
Troubled Debt Restructuring, Charge-offs	262	469
Permanent mortgages guaranteed by U.S. government agencies [Member] | Accruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	73,985	54,322
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	17,274	13,384
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	56,711	40,938
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Permanent mortgages guaranteed by U.S. government agencies [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	1,597
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	179
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	1,418
Troubled Debt Restructuring, Specific allowance	0
Troubled Debt Restructuring, Charge-offs	0
Home equity | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	5,184	4,045
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	3,736	3,531
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	1,448	514
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	247	112
Consumer [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	419	1,008
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	253	758
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	166	250
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	$ 1	$ 1