Loans and Allowance for Credit Losses, Impaired Loans (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2019		Sep. 30, 2019		Dec. 31, 2018
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		$ 446,335		$ 446,335		$ 423,787
Impaired loans, recorded investment, total		357,898		357,898		346,981
Impaired loans, recorded investment with no related allowance		331,468		331,468		311,526
Impaired loans, recorded investment with related allowance		26,430		26,430		35,455
Impaired loans, related allowance		7,533		7,533		8,732
Impaired loans, average recorded investment		367,895		349,646
Impaired loans, interest income recognized		2,300		6,757
Commercial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		186,205		186,205		156,163
Impaired loans, recorded investment, total		111,706		111,706		99,841
Impaired loans, recorded investment with no related allowance		85,276		85,276		64,386
Impaired loans, recorded investment with related allowance		26,430		26,430		35,455
Impaired loans, related allowance		7,533		7,533		8,732
Impaired loans, average recorded investment		117,551		99,544
Impaired loans, interest income recognized		0		0
Commercial [Member] | Energy [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		139,897		139,897		79,675
Impaired loans, recorded investment, total		88,894		88,894		47,494
Impaired loans, recorded investment with no related allowance		62,981		62,981		18,639
Impaired loans, recorded investment with related allowance		25,913		25,913		28,855
Impaired loans, related allowance		7,176		7,176		5,362
Impaired loans, average recorded investment		80,263		67,705
Impaired loans, interest income recognized		0		0
Commercial [Member] | Services [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		9,390		9,390		13,437
Impaired loans, recorded investment, total		6,119		6,119		8,567
Impaired loans, recorded investment with no related allowance		6,093		6,093		8,489
Impaired loans, recorded investment with related allowance		26		26		78
Impaired loans, related allowance		26		26		74
Impaired loans, average recorded investment		8,103		5,172
Impaired loans, interest income recognized		0		0
Commercial [Member] | Wholesale/retail [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		1,718		1,718		1,722
Impaired loans, recorded investment, total		1,504		1,504		1,316
Impaired loans, recorded investment with no related allowance		1,243		1,243		1,015
Impaired loans, recorded investment with related allowance		261		261		301
Impaired loans, related allowance		101		101		101
Impaired loans, average recorded investment		1,447		1,087
Impaired loans, interest income recognized		0		0
Commercial [Member] | Manufacturing [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		9,153	[1]	9,153	[1]	10,055
Impaired loans, recorded investment, total		8,741	[1]	8,741	[1]	8,919
Impaired loans, recorded investment with no related allowance		8,511	[1]	8,511	[1]	8,673
Impaired loans, recorded investment with related allowance		230	[1]	230	[1]	246
Impaired loans, related allowance		230	[1]	230	[1]	246
Impaired loans, average recorded investment	[1]	8,677		8,448
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		17,786		17,786		24,319
Impaired loans, recorded investment, total		5,978		5,978		16,538
Impaired loans, recorded investment with no related allowance		5,978		5,978		10,563
Impaired loans, recorded investment with related allowance		0		0		5,975
Impaired loans, related allowance		0		0		2,949
Impaired loans, average recorded investment		11,063		8,547
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		8,261		8,261		26,955
Impaired loans, recorded investment, total		470		470		17,007
Impaired loans, recorded investment with no related allowance		470		470		17,007
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		7,998		8,585
Impaired loans, interest income recognized		0		0
Commercial real estate [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		24,685		24,685		30,138
Impaired loans, recorded investment, total		23,185		23,185		21,621
Impaired loans, recorded investment with no related allowance		23,185		23,185		21,621
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		22,427		22,403
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		20,516		20,516		27,680
Impaired loans, recorded investment, total		20,132		20,132		20,279
Impaired loans, recorded investment with no related allowance		20,132		20,132		20,279
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		20,094		20,206
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		286		286		301
Impaired loans, recorded investment, total		286		286		301
Impaired loans, recorded investment with no related allowance		286		286		301
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		281		294
Impaired loans, interest income recognized		0		0
Commercial real estate [Member] | Industrial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		909		909		0
Impaired loans, recorded investment, total		909		909		0
Impaired loans, recorded investment with no related allowance		909		909		0
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		454		454
Impaired loans, interest income recognized		0		0
Commercial real estate [Member] | Other commercial real estate [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		813		813		851
Impaired loans, recorded investment, total		653		653		691
Impaired loans, recorded investment with no related allowance		653		653		691
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		393		672
Impaired loans, interest income recognized		0		0
Residential mortgage [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		235,107		235,107		237,208
Impaired loans, recorded investment, total		222,736		222,736		225,289
Impaired loans, recorded investment with no related allowance		222,736		222,736		225,289
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		227,663		227,448
Impaired loans, interest income recognized		2,300		6,757
Residential mortgage [Member] | Permanent mortgage [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		24,639		24,639		28,716
Impaired loans, recorded investment, total		20,165		20,165		23,951
Impaired loans, recorded investment with no related allowance		20,165		20,165		23,951
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		20,984		22,058
Impaired loans, interest income recognized		280		894
Residential mortgage [Member] | Permanent mortgages guaranteed by US government agencies [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		197,847	[2]	197,847	[2]	196,296	[3]
Impaired loans, recorded investment, total		191,764	[2]	191,764	[2]	190,866	[3]
Impaired loans, recorded investment with no related allowance		191,764	[2]	191,764	[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]	196,310		194,751
Impaired loans, interest income recognized	[2]	2,020		5,863
Residential mortgage [Member] | Home equity [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		12,621		12,621		12,196
Impaired loans, recorded investment, total		10,807		10,807		10,472
Impaired loans, recorded investment with no related allowance		10,807		10,807		10,472
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		0
Impaired loans, average recorded investment		10,369		10,639
Impaired loans, interest income recognized		0		0
Personal [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance		338		338		278
Impaired loans, recorded investment, total		271		271		230
Impaired loans, recorded investment with no related allowance		271		271		230
Impaired loans, recorded investment with related allowance		0		0		0
Impaired loans, related allowance		0		0		$ 0
Impaired loans, average recorded investment		254		251
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 September 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 September 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.