Loans and Allowance for Credit Losses, Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2017		Sep. 30, 2016		Dec. 31, 2016
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	$ 460,466		$ 489,949		$ 460,466		$ 489,949		$ 473,526
Impaired loans, recorded investment, total	404,115		411,829		404,115		411,829		418,525
Impaired loans, recorded investment with no related allowance	314,610		369,054		314,610		369,054		407,363
Impaired loans, recorded investment with related allowance	89,505		42,775		89,505		42,775		11,162
Impaired loans, related allowance	13,284		6,564		13,284		6,564		843
Impaired loans, average recorded investment	415,027		415,029		417,476		350,511
Impaired loans, interest income recognized	2,199		2,390		6,721		6,816
Commercial
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	218,386		230,950		218,386		230,950		211,762
Impaired loans, recorded investment, total	176,900		176,464		176,900		176,464		178,953
Impaired loans, recorded investment with no related allowance	87,395		133,798		87,395		133,798		167,837
Impaired loans, recorded investment with related allowance	89,505		42,666		89,505		42,666		11,116
Impaired loans, related allowance	13,284		6,502		13,284		6,502		797
Impaired loans, average recorded investment	187,029		179,227		177,927		109,701
Impaired loans, interest income recognized	0		0		0		0
Commercial | Energy [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	133,643		179,578		133,643		179,578		146,897
Impaired loans, recorded investment, total	110,683		142,966		110,683		142,966		132,499
Impaired loans, recorded investment with no related allowance	45,169		100,300		45,169		100,300		121,418
Impaired loans, recorded investment with related allowance	65,514		42,666		65,514		42,666		11,081
Impaired loans, related allowance	4,944		6,502		4,944		6,502		762
Impaired loans, average recorded investment	117,338		155,555		121,591		85,333
Impaired loans, interest income recognized	0		0		0		0
Commercial | Services [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	3,838		11,858		3,838		11,858		11,723
Impaired loans, recorded investment, total	1,174		8,477		1,174		8,477		8,173
Impaired loans, recorded investment with no related allowance	1,174		8,477		1,174		8,477		8,173
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	4,464		8,932		4,674		9,384
Impaired loans, interest income recognized	0		0		0		0
Commercial | Wholesale/retail [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	8,418		8,528		8,418		8,528		17,669
Impaired loans, recorded investment, total	1,893		2,453		1,893		2,453		11,407
Impaired loans, recorded investment with no related allowance	1,893		2,453		1,893		2,453		11,407
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	6,256		2,613		6,650		2,686
Impaired loans, interest income recognized	0		0		0		0
Commercial | Manufacturing [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	9,674		642		9,674		642		5,320
Impaired loans, recorded investment, total	9,059		274		9,059		274		4,931
Impaired loans, recorded investment with no related allowance	9,059		274		9,059		274		4,931
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	9,357		284		6,995		303
Impaired loans, interest income recognized	0		0		0		0
Commercial | Healthcare [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	24,591		1,168		24,591		1,168		1,147
Impaired loans, recorded investment, total	24,446		855		24,446		855		825
Impaired loans, recorded investment with no related allowance	474		855		474		855		825
Impaired loans, recorded investment with related allowance	23,972		0		23,972		0		0
Impaired loans, related allowance	8,323		0		8,323		0		0
Impaired loans, average recorded investment	24,476		865		12,635		964
Impaired loans, interest income recognized	0		0		0		0
Commercial | Other commercial and industrial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	38,222		29,176		38,222		29,176		29,006
Impaired loans, recorded investment, total	29,645		21,439		29,645		21,439		21,118
Impaired loans, recorded investment with no related allowance	29,626		21,439		29,626		21,439		21,083
Impaired loans, recorded investment with related allowance	19		0		19		0		35
Impaired loans, related allowance	17		0		17		0		35
Impaired loans, average recorded investment	25,138		10,978		25,382		11,031
Impaired loans, interest income recognized	0		0		0		0
Commercial real estate
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	5,003		17,642		5,003		17,642		14,427
Impaired loans, recorded investment, total	2,975		7,350		2,975		7,350		5,521
Impaired loans, recorded investment with no related allowance	2,975		7,350		2,975		7,350		5,521
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	3,375		7,565		4,250		8,176
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	3,532		6,090		3,532		6,090		4,951
Impaired loans, recorded investment, total	1,924		3,739		1,924		3,739		3,433
Impaired loans, recorded investment with no related allowance	1,924		3,739		1,924		3,739		3,433
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	1,988		4,000		2,679		4,074
Impaired loans, interest income recognized	0		0		0		0
Commercial real estate | Retail [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	513		1,914		513		1,914		530
Impaired loans, recorded investment, total	289		1,249		289		1,249		326
Impaired loans, recorded investment with no related allowance	289		1,249		289		1,249		326
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	295		1,257		308		1,284
Impaired loans, interest income recognized	0		0		0		0
Commercial real estate | Office [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	287		1,187		287		1,187		521
Impaired loans, recorded investment, total	275		882		275		882		426
Impaired loans, recorded investment with no related allowance	275		882		275		882		426
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	335		744		351		766
Impaired loans, interest income recognized	0		0		0		0
Commercial real estate | Multifamily [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	0		1,000		0		1,000		1,000
Impaired loans, recorded investment, total	0		51		0		51		38
Impaired loans, recorded investment with no related allowance	0		51		0		51		38
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	5		58		19		163
Impaired loans, interest income recognized	0		0		0		0
Commercial real estate | Industrial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	0		76		0		76		76
Impaired loans, recorded investment, total	0		76		0		76		76
Impaired loans, recorded investment with no related allowance	0		76		0		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	0		76		38		76
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	671		7,375		671		7,375		7,349
Impaired loans, recorded investment, total	487		1,353		487		1,353		1,222
Impaired loans, recorded investment with no related allowance	487		1,353		487		1,353		1,222
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	752		1,430		855		1,813
Impaired loans, interest income recognized	0		0		0		0
Residential mortgage
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	236,787		240,633		236,787		240,633		247,005
Impaired loans, recorded investment, total	223,985		227,329		223,985		227,329		233,761
Impaired loans, recorded investment with no related allowance	223,985		227,220		223,985		227,220		233,715
Impaired loans, recorded investment with related allowance	0		109		0		109		46
Impaired loans, related allowance	0		62		0		62		46
Impaired loans, average recorded investment	224,360		227,717		235,026		232,059
Impaired loans, interest income recognized	2,199		2,390		6,721		6,816
Residential mortgage | Permanent mortgage [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	29,861		32,372		29,861		32,372		28,830
Impaired loans, recorded investment, total	24,623		25,956		24,623		25,956		22,855
Impaired loans, recorded investment with no related allowance	24,623		25,847		24,623		25,847		22,809
Impaired loans, recorded investment with related allowance	0		109		0		109		46
Impaired loans, related allowance	0		62		0		62		46
Impaired loans, average recorded investment	24,019		26,592		23,739		27,470
Impaired loans, interest income recognized	315		292		912		923
Residential mortgage | Permanent mortgages guaranteed by US government agencies [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	193,594	[1]	196,162	[2]	193,594	[1]	196,162	[2]	205,564	[3]
Impaired loans, recorded investment, total	187,370	[1]	190,309	[2]	187,370	[1]	190,309	[2]	199,387	[3]
Impaired loans, recorded investment with no related allowance	187,370	[1]	190,309	[2]	187,370	[1]	190,309	[2]	199,387	[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	188,461	[1]	190,547	[2]	199,532	[1]	193,879	[2]
Impaired loans, interest income recognized	1,884	[1]	2,098	[2]	5,809	[1]	5,893	[2]
Residential mortgage | Home equity [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	13,332		12,099		13,332		12,099		12,611
Impaired loans, recorded investment, total	11,992		11,064		11,992		11,064		11,519
Impaired loans, recorded investment with no related allowance	11,992		11,064		11,992		11,064		11,519
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	11,880		10,578		11,755		10,710
Impaired loans, interest income recognized	0		0		0		0
Personal
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	290		724		290		724		332
Impaired loans, recorded investment, total	255		686		255		686		290
Impaired loans, recorded investment with no related allowance	255		686		255		686		290
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	263		520		273		575
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, 2017, $8.9 million of these loans were nonaccruing and $178 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, 2016, $15 million of these loans were nonaccruing and $175 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, 2016, $12 million of these loans were nonaccruing and $188 million were accruing based on the guarantee by U.S. government agencies.