Loans and Allowances for Credit Losses, Impaired Loans (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	$ 330,630		$ 319,534
Impaired loans, recorded investment, total	283,009		281,970
Impaired loans, recorded investment with no related allowance	281,813		279,827
Impaired loans, recorded investment with related allowance	1,196		2,143
Impaired loans, related allowance	312		954
Impaired loans, average recorded investment	282,731		282,658
Impaired loans, interest income recognized	9,760		8,543
Commercial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	30,742		30,826
Impaired loans, recorded investment, total	13,527		16,760
Impaired loans, recorded investment with no related allowance	12,781		15,549
Impaired loans, recorded investment with related allowance	746		1,211
Impaired loans, related allowance	166		573
Impaired loans, average recorded investment	15,143		20,614
Impaired loans, interest income recognized	0		0
Energy [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	1,444		1,860
Impaired loans, recorded investment, total	1,416		1,860
Impaired loans, recorded investment with no related allowance	1,416		1,860
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	1,638		2,160
Impaired loans, interest income recognized	0		0
Services [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	8,068		6,486
Impaired loans, recorded investment, total	5,201		4,922
Impaired loans, recorded investment with no related allowance	4,487		3,791
Impaired loans, recorded investment with related allowance	714		1,131
Impaired loans, related allowance	157		516
Impaired loans, average recorded investment	5,061		8,506
Impaired loans, interest income recognized	0		0
Wholesale/retail [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	9,457		11,009
Impaired loans, recorded investment, total	4,149		6,969
Impaired loans, recorded investment with no related allowance	4,117		6,937
Impaired loans, recorded investment with related allowance	32		32
Impaired loans, related allowance	9		9
Impaired loans, average recorded investment	5,559		5,023
Impaired loans, interest income recognized	0		0
Manufacturing [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	737		746
Impaired loans, recorded investment, total	450		592
Impaired loans, recorded investment with no related allowance	450		592
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	521		1,300
Impaired loans, interest income recognized	0		0
Healthcare [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	2,432		2,193
Impaired loans, recorded investment, total	1,380		1,586
Impaired loans, recorded investment with no related allowance	1,380		1,538
Impaired loans, recorded investment with related allowance	0		48
Impaired loans, related allowance	0		48
Impaired loans, average recorded investment	1,483		2,376
Impaired loans, interest income recognized	0		0
Other commercial and industrial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	8,604		8,532
Impaired loans, recorded investment, total	931		831
Impaired loans, recorded investment with no related allowance	931		831
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	881		1,249
Impaired loans, interest income recognized	0		0
Commercial Real Estate [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	33,390		49,637
Impaired loans, recorded investment, total	18,557		40,850
Impaired loans, recorded investment with no related allowance	18,277		40,328
Impaired loans, recorded investment with related allowance	280		522
Impaired loans, related allowance	41		133
Impaired loans, average recorded investment	29,703		50,739
Impaired loans, interest income recognized	0		0
Residential construction and land development [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	10,071		20,804
Impaired loans, recorded investment, total	5,299		17,377
Impaired loans, recorded investment with no related allowance	5,192		17,050
Impaired loans, recorded investment with related allowance	107		327
Impaired loans, related allowance	23		107
Impaired loans, average recorded investment	11,338		21,754
Impaired loans, interest income recognized	0		0
Retail [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	5,406		6,133
Impaired loans, recorded investment, total	3,926		4,857
Impaired loans, recorded investment with no related allowance	3,926		4,857
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	4,392		6,487
Impaired loans, interest income recognized	0		0
Office [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	5,959		7,848
Impaired loans, recorded investment, total	3,420		6,391
Impaired loans, recorded investment with no related allowance	3,420		6,383
Impaired loans, recorded investment with related allowance	0		8
Impaired loans, related allowance	0		8
Impaired loans, average recorded investment	4,905		6,610
Impaired loans, interest income recognized	0		0
Multifamily [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	0		7
Impaired loans, recorded investment, total	0		7
Impaired loans, recorded investment with no related allowance	0		7
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	3		1,357
Impaired loans, interest income recognized	0		0
Industrial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	0		252
Impaired loans, recorded investment, total	0		252
Impaired loans, recorded investment with no related allowance	0		252
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	126		2,110
Impaired loans, interest income recognized	0		0
Other commercial real estate [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	11,954		14,593
Impaired loans, recorded investment, total	5,912		11,966
Impaired loans, recorded investment with no related allowance	5,739		11,779
Impaired loans, recorded investment with related allowance	173		187
Impaired loans, related allowance	18		18
Impaired loans, average recorded investment	8,939		12,421
Impaired loans, interest income recognized	0		0
Residential Mortgage [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	265,914		237,843
Impaired loans, recorded investment, total	250,359		223,141
Impaired loans, recorded investment with no related allowance	250,189		222,731
Impaired loans, recorded investment with related allowance	170		410
Impaired loans, related allowance	105		248
Impaired loans, average recorded investment	236,992		209,340
Impaired loans, interest income recognized	9,760		8,543
Permanent mortgage [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	43,463		41,870
Impaired loans, recorded investment, total	34,845		34,279
Impaired loans, recorded investment with no related allowance	34,675		33,869
Impaired loans, recorded investment with related allowance	170		410
Impaired loans, related allowance	105		248
Impaired loans, average recorded investment	34,561		37,071
Impaired loans, interest income recognized	1,418		1,582
Permanent mortgages guaranteed by U.S. government agencies [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	212,684	[1]	188,436	[2]
Impaired loans, recorded investment, total	205,950	[1]	181,598	[2]
Impaired loans, recorded investment with no related allowance	205,950	[1]	181,598	[2]
Impaired loans, recorded investment with related allowance	0	[1]	0	[2]
Impaired loans, related allowance	0	[1]	0	[2]
Impaired loans, average recorded investment	194,017	[1]	165,509	[2]
Impaired loans, interest income recognized	8,342	[1]	6,961	[2]
Home equity
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	9,767		7,537
Impaired loans, recorded investment, total	9,564		7,264
Impaired loans, recorded investment with no related allowance	9,564		7,264
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	8,414		6,760
Impaired loans, interest income recognized	0		0
Consumer [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	584		1,228
Impaired loans, recorded investment, total	566		1,219
Impaired loans, recorded investment with no related allowance	566		1,219
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	893		1,965
Impaired loans, interest income recognized	$ 0		$ 0

[1] 1 All permanent mortgage loans guaranteed by U.S. government agencies are considered impaired as we do not expect full collection of contractual principal and interest. At December 31, 2014, $3.7 million of these loans are nonaccruing and $202 million are accruing based on the guarantee by U.S. government agencies.

[2] 1 All permanent mortgage loans guaranteed by U.S. government agencies are considered impaired as we do not expect full collection of contractual principal and interest. At December 31, 2013, $777 thousand of these loans are nonaccruing and $181 million are accruing based on the guarantee by U.S. government agencies.