Loans and Allowance for Credit Losses, Impaired Loans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	$ 325,424		$ 335,306		$ 330,630
Impaired loans, recorded investment, total	277,656		287,955		283,009
Impaired loans, recorded investment with no related allowance	276,400		282,448		281,813
Impaired loans, recorded investment with related allowance	1,256		5,507		1,196
Impaired loans, related allowance	317		4,159		312
Impaired loans, average recorded investment	285,063		288,738
Impaired loans, interest income recognized	2,571		2,481
Commercial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	31,436		35,809		30,742
Impaired loans, recorded investment, total	13,880		19,046		13,527
Impaired loans, recorded investment with no related allowance	12,959		14,977		12,781
Impaired loans, recorded investment with related allowance	921		4,069		746
Impaired loans, related allowance	197		3,433		166
Impaired loans, average recorded investment	13,703		17,902
Impaired loans, interest income recognized	0		0
Energy [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	1,884		1,787		1,444
Impaired loans, recorded investment, total	1,875		1,759		1,416
Impaired loans, recorded investment with no related allowance	1,875		1,759		1,416
Impaired loans, recorded investment with related allowance	0		0		0
Impaired loans, related allowance	0		0		0
Impaired loans, average recorded investment	1,646		1,809
Impaired loans, interest income recognized	0		0
Services [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	7,698		7,475		8,068
Impaired loans, recorded investment, total	4,744		4,581		5,201
Impaired loans, recorded investment with no related allowance	4,051		3,544		4,487
Impaired loans, recorded investment with related allowance	693		1,037		714
Impaired loans, related allowance	153		424		157
Impaired loans, average recorded investment	4,972		4,752
Impaired loans, interest income recognized	0		0
Wholesale/retail [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	9,953		11,765		9,457
Impaired loans, recorded investment, total	4,401		6,853		4,149
Impaired loans, recorded investment with no related allowance	4,369		6,821		4,117
Impaired loans, recorded investment with related allowance	32		32		32
Impaired loans, related allowance	9		9		9
Impaired loans, average recorded investment	4,275		6,911
Impaired loans, interest income recognized	0		0
Manufacturing [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	716		3,806		737
Impaired loans, recorded investment, total	417		3,565		450
Impaired loans, recorded investment with no related allowance	417		565		450
Impaired loans, recorded investment with related allowance	0		3,000		0
Impaired loans, related allowance	0		3,000		0
Impaired loans, average recorded investment	433		2,078
Impaired loans, interest income recognized	0		0
Healthcare [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	2,626		2,466		2,432
Impaired loans, recorded investment, total	1,558		1,443		1,380
Impaired loans, recorded investment with no related allowance	1,362		1,443		1,380
Impaired loans, recorded investment with related allowance	196		0		0
Impaired loans, related allowance	35		0		0
Impaired loans, average recorded investment	1,469		1,514
Impaired loans, interest income recognized	0		0
Other commercial and industrial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	8,559		8,510		8,604
Impaired loans, recorded investment, total	885		845		931
Impaired loans, recorded investment with no related allowance	885		845		931
Impaired loans, recorded investment with related allowance	0		0		0
Impaired loans, related allowance	0		0		0
Impaired loans, average recorded investment	908		838
Impaired loans, interest income recognized	0		0
Commercial Real Estate [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	34,233		54,751		33,390
Impaired loans, recorded investment, total	19,902		39,305		18,557
Impaired loans, recorded investment with no related allowance	19,732		38,462		18,277
Impaired loans, recorded investment with related allowance	170		843		280
Impaired loans, related allowance	18		185		41
Impaired loans, average recorded investment	19,230		40,077
Impaired loans, interest income recognized	0		0
Residential construction and land development [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	14,367		20,866		10,071
Impaired loans, recorded investment, total	9,598		16,547		5,299
Impaired loans, recorded investment with no related allowance	9,598		15,893		5,192
Impaired loans, recorded investment with related allowance	0		654		107
Impaired loans, related allowance	0		162		23
Impaired loans, average recorded investment	7,449		16,962
Impaired loans, interest income recognized	0		0
Retail [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	5,376		6,462		5,406
Impaired loans, recorded investment, total	3,857		4,626		3,926
Impaired loans, recorded investment with no related allowance	3,857		4,626		3,926
Impaired loans, recorded investment with related allowance	0		0		0
Impaired loans, related allowance	0		0		0
Impaired loans, average recorded investment	3,892		4,742
Impaired loans, interest income recognized	0		0
Office [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	4,464		8,688		5,959
Impaired loans, recorded investment, total	2,410		6,301		3,420
Impaired loans, recorded investment with no related allowance	2,410		6,296		3,420
Impaired loans, recorded investment with related allowance	0		5		0
Impaired loans, related allowance	0		5		0
Impaired loans, average recorded investment	2,915		6,346
Impaired loans, interest income recognized	0		0
Multifamily [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	0		0		0
Impaired loans, recorded investment, total	0		0		0
Impaired loans, recorded investment with no related allowance	0		0		0
Impaired loans, recorded investment with related allowance	0		0		0
Impaired loans, related allowance	0		0		0
Impaired loans, average recorded investment	0		3
Impaired loans, interest income recognized	0		0
Industrial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	76		1,043		0
Impaired loans, recorded investment, total	76		886		0
Impaired loans, recorded investment with no related allowance	76		886		0
Impaired loans, recorded investment with related allowance	0		0		0
Impaired loans, related allowance	0		0		0
Impaired loans, average recorded investment	38		569
Impaired loans, interest income recognized	0		0
Other commercial real estate [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	9,950		17,692		11,954
Impaired loans, recorded investment, total	3,961		10,945		5,912
Impaired loans, recorded investment with no related allowance	3,791		10,761		5,739
Impaired loans, recorded investment with related allowance	170		184		173
Impaired loans, related allowance	18		18		18
Impaired loans, average recorded investment	4,936		11,455
Impaired loans, interest income recognized	0		0
Residential Mortgage [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	259,273		243,757		265,914
Impaired loans, recorded investment, total	243,410		228,630		250,359
Impaired loans, recorded investment with no related allowance	243,245		228,035		250,189
Impaired loans, recorded investment with related allowance	165		595		170
Impaired loans, related allowance	102		541		105
Impaired loans, average recorded investment	251,615		229,662
Impaired loans, interest income recognized	2,571		2,481
Permanent mortage [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	42,011		45,215		43,463
Impaired loans, recorded investment, total	33,365		36,342		34,845
Impaired loans, recorded investment with no related allowance	33,200		35,747		34,675
Impaired loans, recorded investment with related allowance	165		595		170
Impaired loans, related allowance	102		541		105
Impaired loans, average recorded investment	34,105		35,310
Impaired loans, interest income recognized	315		345
Permanent mortgages guaranteed by US govenment agencies [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	207,133	[1]	191,067	[2]	212,684	[3]
Impaired loans, recorded investment, total	200,179	[1]	184,822	[2]	205,950	[3]
Impaired loans, recorded investment with no related allowance	200,179	[1]	184,822	[2]	205,950	[3]
Impaired loans, recorded investment with related allowance	0	[1]	0	[2]	0	[3]
Impaired loans, related allowance	0	[1]	0	[2]	0	[3]
Impaired loans, average recorded investment	207,795	[1]	186,987	[2]
Impaired loans, interest income recognized	2,256	[1]	2,136	[2]
Home equity {Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	10,129		7,475		9,767
Impaired loans, recorded investment, total	9,866		7,466		9,564
Impaired loans, recorded investment with no related allowance	9,866		7,466		9,564
Impaired loans, recorded investment with related allowance	0		0		0
Impaired loans, related allowance	0		0		0
Impaired loans, average recorded investment	9,715		7,365
Impaired loans, interest income recognized	0		0
Consumer [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	482		989		584
Impaired loans, recorded investment, total	464		974		566
Impaired loans, recorded investment with no related allowance	464		974		566
Impaired loans, recorded investment with related allowance	0		0		0
Impaired loans, related allowance	0		0		0
Impaired loans, average recorded investment	515		1,097
Impaired loans, interest income recognized	$ 0		$ 0

[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 March 31, 2015, $3.3 million of these loans were nonaccruing and $197 million were accruing based on the guarantee by U.S. government agencies.

[2] 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 March 31, 2014, $1.6 million of these loans were nonaccruing and $183 million were accruing based on the guarantee by U.S. government agencies.

[3] 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 were nonaccruing and $202 million were accruing based on the guarantee by U.S. government agencies.