Loans and Allowance for Credit Losses, Impaired Loans (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019		Jun. 30, 2019		Dec. 31, 2018
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		$ 461,668		$ 461,668		$ 423,787
Impaired loans, recorded investment, total		372,409		372,409		346,981
Impaired loans, recorded investment with no related allowance		363,147		363,147		311,526
Impaired loans, recorded investment with related allowance		9,262		9,262		35,455
Impaired loans, related allowance		4,038		4,038		8,732
Impaired loans, average recorded investment		358,043		354,305
Impaired loans, interest income recognized		2,254		4,457
Commercial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		198,891		198,891		156,163
Impaired loans, recorded investment, total		123,395		123,395		99,841
Impaired loans, recorded investment with no related allowance		114,133		114,133		64,386
Impaired loans, recorded investment with related allowance		9,262		9,262		35,455
Impaired loans, related allowance		4,038		4,038		8,732
Impaired loans, average recorded investment		112,049		105,389
Impaired loans, interest income recognized		0		0
Commercial [Member] | Energy [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		118,959		118,959		79,675
Impaired loans, recorded investment, total		71,632		71,632		47,494
Impaired loans, recorded investment with no related allowance		64,066		64,066		18,639
Impaired loans, recorded investment with related allowance		7,566		7,566		28,855
Impaired loans, related allowance		1,175		1,175		5,362
Impaired loans, average recorded investment		58,185		59,074
Impaired loans, interest income recognized		0		0
Commercial [Member] | Services [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		13,343		13,343		13,437
Impaired loans, recorded investment, total		10,087		10,087		8,567
Impaired loans, recorded investment with no related allowance		10,061		10,061		8,489
Impaired loans, recorded investment with related allowance		26		26		78
Impaired loans, related allowance		26		26		74
Impaired loans, average recorded investment		10,309		7,156
Impaired loans, interest income recognized		0		0
Commercial [Member] | Wholesale/retail [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		1,600		1,600		1,722
Impaired loans, recorded investment, total		1,390		1,390		1,316
Impaired loans, recorded investment with no related allowance		1,126		1,126		1,015
Impaired loans, recorded investment with related allowance		264		264		301
Impaired loans, related allowance		101		101		101
Impaired loans, average recorded investment		1,407		1,030
Impaired loans, interest income recognized		0		0
Commercial [Member] | Manufacturing [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		8,896	[1]	8,896	[1]	10,055
Impaired loans, recorded investment, total		8,613	[1]	8,613	[1]	8,919
Impaired loans, recorded investment with no related allowance		8,383	[1]	8,383	[1]	8,673
Impaired loans, recorded investment with related allowance		230	[1]	230	[1]	246
Impaired loans, related allowance		236	[1]	236	[1]	246
Impaired loans, average recorded investment	[1]	9,080		8,384
Impaired loans, interest income recognized	[1]	0		0
Impaired loans, unpaid principal balance to affiliates		4,700		4,700
Commercial [Member] | Healthcare [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		30,255		30,255		24,319
Impaired loans, recorded investment, total		16,148		16,148		16,538
Impaired loans, recorded investment with no related allowance		14,972		14,972		10,563
Impaired loans, recorded investment with related allowance		1,176		1,176		5,975
Impaired loans, related allowance		2,500		2,500		2,949
Impaired loans, average recorded investment		17,441		13,632
Impaired loans, interest income recognized		0		0
Commercial [Member] | Public finance [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
Impaired loans, interest income recognized		0		0
Commercial [Member] | Other commercial and industrial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		25,838		25,838		26,955
Impaired loans, recorded investment, total		15,525		15,525		17,007
Impaired loans, recorded investment with no related allowance		15,525		15,525		17,007
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		15,627		16,113
Impaired loans, interest income recognized		0		0
Commercial real estate [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		23,109		23,109		30,138
Impaired loans, recorded investment, total		21,670		21,670		21,621
Impaired loans, recorded investment with no related allowance		21,670		21,670		21,621
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		21,590		21,645
Impaired loans, interest income recognized		0		0
Commercial real estate [Member] | Residential construction and land development [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		1,306		1,306		1,306
Impaired loans, recorded investment, total		350		350		350
Impaired loans, recorded investment with no related allowance		350		350		350
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		350		350
Impaired loans, interest income recognized		0		0
Commercial real estate [Member] | Retail [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		20,380		20,380		27,680
Impaired loans, recorded investment, total		20,057		20,057		20,279
Impaired loans, recorded investment with no related allowance		20,057		20,057		20,279
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		20,108		20,168
Impaired loans, interest income recognized		0		0
Commercial real estate [Member] | Office [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		855		855		0
Impaired loans, recorded investment, total		855		855		0
Impaired loans, recorded investment with no related allowance		855		855		0
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		855		427
Impaired loans, interest income recognized		0		0
Commercial real estate [Member] | Multifamily [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		275		275		301
Impaired loans, recorded investment, total		275		275		301
Impaired loans, recorded investment with no related allowance		275		275		301
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		138		288
Impaired loans, interest income recognized		0		0
Commercial real estate [Member] | Industrial [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		0
Impaired loans, interest income recognized		0		0
Commercial real estate [Member] | Other commercial real estate [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		293		293		851
Impaired loans, recorded investment, total		133		133		691
Impaired loans, recorded investment with no related allowance		133		133		691
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		139		412
Impaired loans, interest income recognized		0		0
Residential mortgage [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		239,379		239,379		237,208
Impaired loans, recorded investment, total		227,107		227,107		225,289
Impaired loans, recorded investment with no related allowance		227,107		227,107		225,289
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		224,135		227,037
Impaired loans, interest income recognized		2,254		4,457
Residential mortgage [Member] | Permanent mortgage [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		26,434		26,434		28,716
Impaired loans, recorded investment, total		21,803		21,803		23,951
Impaired loans, recorded investment with no related allowance		21,803		21,803		23,951
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		22,370		22,877
Impaired loans, interest income recognized		316		614
Residential mortgage [Member] | Permanent mortgages guaranteed by US government agencies [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		201,217	[2]	201,217	[2]	196,296	[3]
Impaired loans, recorded investment, total		195,373	[2]	195,373	[2]	190,866	[3]
Impaired loans, recorded investment with no related allowance		195,373	[2]	195,373	[2]	190,866	[3]
Impaired loans, recorded investment with related allowance		0	[2]	0	[2]	0	[3]
Impaired loans, related allowance		0	[2]	0	[2]	0	[3]
Impaired loans, average recorded investment	[2]	191,537		193,958
Impaired loans, interest income recognized	[2]	1,938		3,843
Residential mortgage [Member] | Home equity [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		11,728		11,728		12,196
Impaired loans, recorded investment, total		9,931		9,931		10,472
Impaired loans, recorded investment with no related allowance		9,931		9,931		10,472
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		10,228		10,202
Impaired loans, interest income recognized		0		0
Personal [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		289		289		278
Impaired loans, recorded investment, total		237		237		230
Impaired loans, recorded investment with no related allowance		237		237		230
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		$ 0
Impaired loans, average recorded investment		269		234
Impaired loans, interest income recognized		$ 0		$ 0

[1] Impaired manufacturing sector loans included $4.7 million of loans from an affiliated entity, with no allowance as the fair value of the collateral exceeded the outstanding principal balance at June 30, 2019.

[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 June 30, 2019, the majority 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, 2018, the majority were accruing based on the guarantee by U.S. government agencies.