Loans and Allowance for Credit Losses, Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	$ 415,920	$ 423,787
Impaired loans, recorded investment, total	338,939	346,981
Impaired loans, recorded investment with no related allowance	330,891	311,526
Impaired loans, recorded investment with related allowance	8,048	35,455
Impaired loans, related allowance	3,543	8,732
Impaired loans, average recorded investment	346,225
Impaired loans, interest income recognized	2,203
Commercial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	153,786	156,163
Impaired loans, recorded investment, total	90,358	99,841
Impaired loans, recorded investment with no related allowance	82,310	64,386
Impaired loans, recorded investment with related allowance	8,048	35,455
Impaired loans, related allowance	3,543	8,732
Impaired loans, average recorded investment	94,044
Impaired loans, interest income recognized	0
Commercial [Member] | Energy [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	72,615	79,675
Impaired loans, recorded investment, total	35,332	47,494
Impaired loans, recorded investment with no related allowance	31,332	18,639
Impaired loans, recorded investment with related allowance	4,000	28,855
Impaired loans, related allowance	675	5,362
Impaired loans, average recorded investment	45,627
Impaired loans, interest income recognized	0
Commercial [Member] | Services [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	13,744	13,437
Impaired loans, recorded investment, total	9,555	8,567
Impaired loans, recorded investment with no related allowance	9,529	8,489
Impaired loans, recorded investment with related allowance	26	78
Impaired loans, related allowance	26	74
Impaired loans, average recorded investment	7,378
Impaired loans, interest income recognized	0
Commercial [Member] | Wholesale/retail [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	1,642	1,722
Impaired loans, recorded investment, total	1,425	1,316
Impaired loans, recorded investment with no related allowance	1,142	1,015
Impaired loans, recorded investment with related allowance	283	301
Impaired loans, related allowance	101	101
Impaired loans, average recorded investment	1,047
Impaired loans, interest income recognized	0
Commercial [Member] | Manufacturing [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	9,697	10,055
Impaired loans, recorded investment, total	9,548	8,919
Impaired loans, recorded investment with no related allowance	9,307	8,673
Impaired loans, recorded investment with related allowance	241	246
Impaired loans, related allowance	241	246
Impaired loans, average recorded investment	8,851
Impaired loans, interest income recognized	0
Impaired loans, unpaid principal balance to affiliates	4,700
Commercial [Member] | Healthcare [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	30,189	24,319
Impaired loans, recorded investment, total	18,768	16,538
Impaired loans, recorded investment with no related allowance	15,270	10,563
Impaired loans, recorded investment with related allowance	3,498	5,975
Impaired loans, related allowance	2,500	2,949
Impaired loans, average recorded investment	14,926
Impaired loans, interest income recognized	0
Commercial [Member] | Public finance [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	0	0
Impaired loans, recorded investment, total	0	0
Impaired loans, recorded investment with no related allowance	0	0
Impaired loans, recorded investment with related allowance	0	0
Impaired loans, related allowance	0	0
Impaired loans, average recorded investment	0
Commercial [Member] | Other commercial and industrial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	25,899	26,955
Impaired loans, recorded investment, total	15,730	17,007
Impaired loans, recorded investment with no related allowance	15,730	17,007
Impaired loans, recorded investment with related allowance	0	0
Impaired loans, related allowance	0	0
Impaired loans, average recorded investment	16,215
Impaired loans, interest income recognized	0
Commercial real estate [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	22,957	30,138
Impaired loans, recorded investment, total	21,508	21,621
Impaired loans, recorded investment with no related allowance	21,508	21,621
Impaired loans, recorded investment with related allowance	0	0
Impaired loans, related allowance	0	0
Impaired loans, average recorded investment	21,565
Impaired loans, interest income recognized	0
Commercial real estate [Member] | Residential construction and land development [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	1,306	1,306
Impaired loans, recorded investment, total	350	350
Impaired loans, recorded investment with no related allowance	350	350
Impaired loans, recorded investment with related allowance	0	0
Impaired loans, related allowance	0	0
Impaired loans, average recorded investment	350
Impaired loans, interest income recognized	0
Commercial real estate [Member] | Retail [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	20,491	27,680
Impaired loans, recorded investment, total	20,159	20,279
Impaired loans, recorded investment with no related allowance	20,159	20,279
Impaired loans, recorded investment with related allowance	0	0
Impaired loans, related allowance	0	0
Impaired loans, average recorded investment	20,219
Impaired loans, interest income recognized	0
Commercial real estate [Member] | Office [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	855	0
Impaired loans, recorded investment, total	855	0
Impaired loans, recorded investment with no related allowance	855	0
Impaired loans, recorded investment with related allowance	0	0
Impaired loans, related allowance	0	0
Impaired loans, average recorded investment	427
Impaired loans, interest income recognized	0
Commercial real estate [Member] | Multifamily [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	0	301
Impaired loans, recorded investment, total	0	301
Impaired loans, recorded investment with no related allowance	0	301
Impaired loans, recorded investment with related allowance	0	0
Impaired loans, related allowance	0	0
Impaired loans, average recorded investment	151
Impaired loans, interest income recognized	0
Commercial real estate [Member] | Industrial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	0	0
Impaired loans, recorded investment, total	0	0
Impaired loans, recorded investment with no related allowance	0	0
Impaired loans, recorded investment with related allowance	0	0
Impaired loans, related allowance	0	0
Impaired loans, average recorded investment	0
Impaired loans, interest income recognized	0
Commercial real estate [Member] | Other commercial real estate [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	305	851
Impaired loans, recorded investment, total	144	691
Impaired loans, recorded investment with no related allowance	144	691
Impaired loans, recorded investment with related allowance	0	0
Impaired loans, related allowance	0	0
Impaired loans, average recorded investment	418
Impaired loans, interest income recognized	0
Residential mortgage [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	238,819	237,208
Impaired loans, recorded investment, total	226,771	225,289
Impaired loans, recorded investment with no related allowance	226,771	225,289
Impaired loans, recorded investment with related allowance	0	0
Impaired loans, related allowance	0	0
Impaired loans, average recorded investment	230,350
Impaired loans, interest income recognized	2,203
Residential mortgage [Member] | Permanent mortgage [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	27,658	28,716
Impaired loans, recorded investment, total	22,937	23,951
Impaired loans, recorded investment with no related allowance	22,937	23,951
Impaired loans, recorded investment with related allowance	0	0
Impaired loans, related allowance	0	0
Impaired loans, average recorded investment	23,444
Impaired loans, interest income recognized	298
Residential mortgage [Member] | Permanent mortgages guaranteed by US government agencies [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	198,882	196,296
Impaired loans, recorded investment, total	193,308	190,866
Impaired loans, recorded investment with no related allowance	193,308	190,866
Impaired loans, recorded investment with related allowance	0	0
Impaired loans, related allowance	0	0
Impaired loans, average recorded investment	196,407
Impaired loans, interest income recognized	1,905
Residential mortgage [Member] | Home equity [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	12,279	12,196
Impaired loans, recorded investment, total	10,526	10,472
Impaired loans, recorded investment with no related allowance	10,526	10,472
Impaired loans, recorded investment with related allowance	0	0
Impaired loans, related allowance	0	0
Impaired loans, average recorded investment	10,499
Impaired loans, interest income recognized	0
Personal [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	358	278
Impaired loans, recorded investment, total	302	230
Impaired loans, recorded investment with no related allowance	302	230
Impaired loans, recorded investment with related allowance	0	0
Impaired loans, related allowance	0	$ 0
Impaired loans, average recorded investment	266
Impaired loans, interest income recognized	$ 0