Loans and Allowance for Credit Losses, Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2016		Sep. 30, 2015		Sep. 30, 2016		Sep. 30, 2015		Dec. 31, 2015
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	$ 489,949		$ 323,633		$ 489,949		$ 323,633		$ 369,450
Impaired loans, recorded investment, total	411,829		278,174		411,829		278,174		322,165
Impaired loans, recorded investment with no related allowance	369,054		264,177		369,054		264,177		278,245
Impaired loans, recorded investment with related allowance	42,775		13,997		42,775		13,997		43,920
Impaired loans, related allowance	6,564		4,951		6,564		4,951		16,393
Impaired loans, average recorded investment	415,029		279,484		350,511		279,572
Impaired loans, interest income recognized	2,390		2,199		6,816		7,147
Commercial
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	230,950		51,733		230,950		51,733		96,262
Impaired loans, recorded investment, total	176,464		33,798		176,464		33,798		76,424
Impaired loans, recorded investment with no related allowance	133,798		20,118		133,798		20,118		32,779
Impaired loans, recorded investment with related allowance	42,666		13,680		42,666		13,680		43,645
Impaired loans, related allowance	6,502		4,836		6,502		4,836		16,307
Impaired loans, average recorded investment	179,227		29,015		109,701		23,662
Impaired loans, interest income recognized	0		0		0		0
Commercial | Energy [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	179,578		18,904		179,578		18,904		63,910
Impaired loans, recorded investment, total	142,966		17,880		142,966		17,880		61,189
Impaired loans, recorded investment with no related allowance	100,300		5,017		100,300		5,017		18,330
Impaired loans, recorded investment with related allowance	42,666		12,863		42,666		12,863		42,859
Impaired loans, related allowance	6,502		4,644		6,502		4,644		16,115
Impaired loans, average recorded investment	155,555		12,361		85,333		9,648
Impaired loans, interest income recognized	0		0		0		0
Commercial | Services [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	11,858		13,677		11,858		13,677		13,449
Impaired loans, recorded investment, total	8,477		10,692		8,477		10,692		10,290
Impaired loans, recorded investment with no related allowance	8,477		10,041		8,477		10,041		9,657
Impaired loans, recorded investment with related allowance	0		651		0		651		633
Impaired loans, related allowance	0		148		0		148		148
Impaired loans, average recorded investment	8,932		10,818		9,384		7,946
Impaired loans, interest income recognized	0		0		0		0
Commercial | Wholesale/retail [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	8,528		8,588		8,528		8,588		8,582
Impaired loans, recorded investment, total	2,453		3,058		2,453		3,058		2,919
Impaired loans, recorded investment with no related allowance	2,453		3,046		2,453		3,046		2,907
Impaired loans, recorded investment with related allowance	0		12		0		12		12
Impaired loans, related allowance	0		9		0		9		9
Impaired loans, average recorded investment	2,613		3,612		2,686		3,603
Impaired loans, interest income recognized	0		0		0		0
Commercial | Manufacturing [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	642		675		642		675		665
Impaired loans, recorded investment, total	274		352		274		352		331
Impaired loans, recorded investment with no related allowance	274		352		274		352		331
Impaired loans, recorded investment with related allowance	0		0		0		0		0
Impaired loans, related allowance	0		0		0		0		0
Impaired loans, average recorded investment	284		365		303		401
Impaired loans, interest income recognized	0		0		0		0
Commercial | Healthcare [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	1,168		1,612		1,168		1,612		1,352
Impaired loans, recorded investment, total	855		1,218		855		1,218		1,072
Impaired loans, recorded investment with no related allowance	855		1,064		855		1,064		931
Impaired loans, recorded investment with related allowance	0		154		0		154		141
Impaired loans, related allowance	0		35		0		35		35
Impaired loans, average recorded investment	865		1,248		964		1,299
Impaired loans, interest income recognized	0		0		0		0
Commercial | Other commercial and industrial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	29,176		8,277		29,176		8,277		8,304
Impaired loans, recorded investment, total	21,439		598		21,439		598		623
Impaired loans, recorded investment with no related allowance	21,439		598		21,439		598		623
Impaired loans, recorded investment with related allowance	0		0		0		0		0
Impaired loans, related allowance	0		0		0		0		0
Impaired loans, average recorded investment	10,978		611		11,031		765
Impaired loans, interest income recognized	0		0		0		0
Commercial real estate
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	17,642		23,565		17,642		23,565		21,454
Impaired loans, recorded investment, total	7,350		10,956		7,350		10,956		9,001
Impaired loans, recorded investment with no related allowance	7,350		10,793		7,350		10,793		8,842
Impaired loans, recorded investment with related allowance	0		163		0		163		159
Impaired loans, related allowance	0		18		0		18		18
Impaired loans, average recorded investment	7,565		15,548		8,176		14,756
Impaired loans, interest income recognized	0		0		0		0
Commercial real estate | Residential construction and land development [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	6,090		9,349		6,090		9,349		8,963
Impaired loans, recorded investment, total	3,739		4,748		3,739		4,748		4,409
Impaired loans, recorded investment with no related allowance	3,739		4,748		3,739		4,748		4,409
Impaired loans, recorded investment with related allowance	0		0		0		0		0
Impaired loans, related allowance	0		0		0		0		0
Impaired loans, average recorded investment	4,000		7,058		4,074		5,023
Impaired loans, interest income recognized	0		0		0		0
Commercial real estate | Retail [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	1,914		2,252		1,914		2,252		1,923
Impaired loans, recorded investment, total	1,249		1,648		1,249		1,648		1,319
Impaired loans, recorded investment with no related allowance	1,249		1,648		1,249		1,648		1,319
Impaired loans, recorded investment with related allowance	0		0		0		0		0
Impaired loans, related allowance	0		0		0		0		0
Impaired loans, average recorded investment	1,257		2,737		1,284		2,787
Impaired loans, interest income recognized	0		0		0		0
Commercial real estate | Office [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	1,187		2,046		1,187		2,046		937
Impaired loans, recorded investment, total	882		684		882		684		651
Impaired loans, recorded investment with no related allowance	882		684		882		684		651
Impaired loans, recorded investment with related allowance	0		0		0		0		0
Impaired loans, related allowance	0		0		0		0		0
Impaired loans, average recorded investment	744		1,522		766		2,052
Impaired loans, interest income recognized	0		0		0		0
Commercial real estate | Multifamily [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	1,000		192		1,000		192		1,192
Impaired loans, recorded investment, total	51		185		51		185		274
Impaired loans, recorded investment with no related allowance	51		185		51		185		274
Impaired loans, recorded investment with related allowance	0		0		0		0		0
Impaired loans, related allowance	0		0		0		0		0
Impaired loans, average recorded investment	58		190		163		93
Impaired loans, interest income recognized	0		0		0		0
Commercial real estate | Industrial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	76		76		76		76		76
Impaired loans, recorded investment, total	76		76		76		76		76
Impaired loans, recorded investment with no related allowance	76		76		76		76		76
Impaired loans, recorded investment with related allowance	0		0		0		0		0
Impaired loans, related allowance	0		0		0		0		0
Impaired loans, average recorded investment	76		76		76		38
Impaired loans, interest income recognized	0		0		0		0
Commercial real estate | Other commercial real estate [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	7,375		9,650		7,375		9,650		8,363
Impaired loans, recorded investment, total	1,353		3,615		1,353		3,615		2,272
Impaired loans, recorded investment with no related allowance	1,353		3,452		1,353		3,452		2,113
Impaired loans, recorded investment with related allowance	0		163		0		163		159
Impaired loans, related allowance	0		18		0		18		18
Impaired loans, average recorded investment	1,430		3,965		1,813		4,763
Impaired loans, interest income recognized	0		0		0		0
Residential mortgage
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	240,633		247,819		240,633		247,819		251,245
Impaired loans, recorded investment, total	227,329		232,926		227,329		232,926		236,277
Impaired loans, recorded investment with no related allowance	227,220		232,772		227,220		232,772		236,161
Impaired loans, recorded investment with related allowance	109		154		109		154		116
Impaired loans, related allowance	62		97		62		97		68
Impaired loans, average recorded investment	227,717		234,399		232,059		240,624
Impaired loans, interest income recognized	2,390		2,199		6,816		7,147
Residential mortgage | Permanent mortgage [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	32,372		38,829		32,372		38,829		37,273
Impaired loans, recorded investment, total	25,956		30,660		25,956		30,660		28,984
Impaired loans, recorded investment with no related allowance	25,847		30,506		25,847		30,506		28,868
Impaired loans, recorded investment with related allowance	109		154		109		154		116
Impaired loans, related allowance	62		97		62		97		68
Impaired loans, average recorded investment	26,592		31,424		27,470		32,753
Impaired loans, interest income recognized	292		297		923		942
Residential mortgage | Permanent mortgages guaranteed by US government agencies [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	196,162	[1]	198,905	[2]	196,162	[1]	198,905	[2]	202,984	[3]
Impaired loans, recorded investment, total	190,309	[1]	192,712	[2]	190,309	[1]	192,712	[2]	196,937	[3]
Impaired loans, recorded investment with no related allowance	190,309	[1]	192,712	[2]	190,309	[1]	192,712	[2]	196,937	[3]
Impaired loans, recorded investment with related allowance	0	[1]	0	[2]	0	[1]	0	[2]	0	[3]
Impaired loans, related allowance	0	[1]	0	[2]	0	[1]	0	[2]	0	[3]
Impaired loans, average recorded investment	190,547	[1]	193,165	[2]	193,879	[1]	198,312	[2]
Impaired loans, interest income recognized	2,098	[1]	1,902	[2]	5,893	[1]	6,205	[2]
Residential mortgage | Home equity {Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	12,099		10,085		12,099		10,085		10,988
Impaired loans, recorded investment, total	11,064		9,554		11,064		9,554		10,356
Impaired loans, recorded investment with no related allowance	11,064		9,554		11,064		9,554		10,356
Impaired loans, recorded investment with related allowance	0		0		0		0		0
Impaired loans, related allowance	0		0		0		0		0
Impaired loans, average recorded investment	10,578		9,810		10,710		9,559
Impaired loans, interest income recognized	0		0		0		0
Personal
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	724		516		724		516		489
Impaired loans, recorded investment, total	686		494		686		494		463
Impaired loans, recorded investment with no related allowance	686		494		686		494		463
Impaired loans, recorded investment with related allowance	0		0		0		0		0
Impaired loans, related allowance	0		0		0		0		$ 0
Impaired loans, average recorded investment	520		522		575		530
Impaired loans, interest income recognized	$ 0		$ 0		$ 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 September 30, 2016, $15 million of these loans were nonaccruing and $175 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 September 30, 2015, $3.9 million of these loans were nonaccruing and $189 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, 2015, $22 million of these loans were nonaccruing and $175 million were accruing based on the guarantee by U.S. government agencies.