Loans and Allowances for Credit Losses, Troubled Debt Restructurings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	$ 147,117	$ 127,684
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	74,738	54,131
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	72,379	73,553
Troubled Debt Restructuring, Specific allowance	46	225
Troubled Debt Restructuring, Charge-offs	4,732	1,211
Nonaccrual [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	65,747	53,634
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	47,449	31,102
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	18,298	22,532
Troubled Debt Restructuring, Specific allowance	46	225
Troubled Debt Restructuring, Charge-offs	4,732	1,211
Nonaccrual [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	36,879	15,665
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	29,225	14,264
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	7,654	1,401
Troubled Debt Restructuring, Specific allowance	0	157
Troubled Debt Restructuring, Charge-offs	4,401	928
Nonaccrual [Member] | Commercial [Member] | Energy [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	16,893	2,304
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	10,867	2,304
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	6,026	0
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	4,401	928
Nonaccrual [Member] | Commercial [Member] | Services [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	7,527	9,027
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	6,830	8,210
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	697	817
Troubled Debt Restructuring, Specific allowance	0	148
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial [Member] | Wholesale/retail [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	11,291	2,758
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	11,251	2,706
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	40	52
Troubled Debt Restructuring, Specific allowance	0	9
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial [Member] | Manufacturing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	224	282
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	224	282
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
Nonaccrual [Member] | Commercial [Member] | Healthcare [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	607	673
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	0	673
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	607	0
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial [Member] | Other commercial and industrial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	337	621
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	53	89
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	284	532
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	1,707	4,732
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	1,114	3,141
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	593	1,591
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial Real Estate [Member] | Residential construction and land development [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	690	2,328
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	97	1,556
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	593	772
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial Real Estate [Member] | Retail [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	326	1,319
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	326	942
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	377
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Commercial Real Estate [Member] | Office [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	143	165
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	143	165
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
Nonaccrual [Member] | Commercial Real Estate [Member] | Multifamily [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
Nonaccrual [Member] | Commercial Real Estate [Member] | Industrial [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
Nonaccrual [Member] | Commercial Real Estate [Member] | Other commercial real estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	548	920
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	548	478
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	0	442
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	26,924	32,913
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	16,874	13,400
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	10,050	19,513
Troubled Debt Restructuring, Specific allowance	46	68
Troubled Debt Restructuring, Charge-offs	258	272
Nonaccrual [Member] | Residential Mortgage [Member] | Permanent mortgage [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	14,876	16,618
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	10,175	9,043
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	4,701	7,575
Troubled Debt Restructuring, Specific allowance	46	68
Troubled Debt Restructuring, Charge-offs	28	192
Nonaccrual [Member] | Residential Mortgage [Member] | Permanent mortgages guaranteed by U.S. government agencies [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	6,702	11,136
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	2,241	139
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	4,461	10,997
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Nonaccrual [Member] | Residential Mortgage [Member] | Home equity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	5,346	5,159
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	4,458	4,218
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	888	941
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	230	80
Nonaccrual [Member] | Personal [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	237	324
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	236	297
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	1	27
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	73	11
Accruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	81,370	74,050
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	27,289	23,029
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	54,081	51,021
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Accruing [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	81,370	74,050
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	27,289	23,029
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	54,081	51,021
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	0	0
Accruing [Member] | Residential Mortgage [Member] | Permanent mortgages guaranteed by U.S. government agencies [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	81,370	74,050
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	27,289	23,029
Troubled Debt Restructuring, Not Performing in Accordance With Modified Terms	54,081	51,021
Troubled Debt Restructuring, Specific allowance	0	0
Troubled Debt Restructuring, Charge-offs	$ 0	$ 0