Past Due Loans, Allowance For Credit Losses, Impaired Loans, and TDRS - Aging Analysis of Past Due Loans and Non-Performing Loans by Class (Details) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Current	[1]	$ 12,671,812	$ 11,357,176
Total Past Due		101,507	89,607
Total Loans		12,773,319	11,446,783
Non-accrual		77,692	56,935
90 Days or More Past Due, Still Accruing Interest		4,657	8,282
30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		53,874	40,102
90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		47,633	49,505
Commercial, Industrial, and Agricultural
Financing Receivable, Past Due [Line Items]
Total Loans		4,988,101	4,551,221
Commercial, Industrial, and Agricultural | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Current	[1]	4,537,236	4,085,164
Total Past Due		33,125	35,129
Total Loans		4,570,361	4,120,293
Non-accrual		26,739	33,507
90 Days or More Past Due, Still Accruing Interest		1,982	422
Commercial, Industrial, and Agricultural | Agricultural
Financing Receivable, Past Due [Line Items]
Current	[1]	404,731	428,357
Total Past Due		13,009	2,571
Total Loans		417,740	430,928
Non-accrual		6,242	1,564
90 Days or More Past Due, Still Accruing Interest		23	101
Commercial, Industrial, and Agricultural | 30-89 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Past Due		20,929	8,832
Commercial, Industrial, and Agricultural | 30-89 Days Past Due | Agricultural
Financing Receivable, Past Due [Line Items]
Total Past Due		6,966	940
Commercial, Industrial, and Agricultural | 90 Days or More Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Past Due		12,196	26,297
Commercial, Industrial, and Agricultural | 90 Days or More Past Due | Agricultural
Financing Receivable, Past Due [Line Items]
Total Past Due		6,043	1,631
Commercial real estate
Financing Receivable, Past Due [Line Items]
Current	[1]	4,737,784	4,561,677
Total Past Due		35,085	34,572
Total Loans		4,772,869	4,596,249
Non-accrual		33,796	12,615
90 Days or More Past Due, Still Accruing Interest		1,175	6,467
Commercial real estate | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Current	[1]	1,869,816	1,803,059
Total Past Due		23,061	17,858
Total Loans		1,892,877	1,820,917
Non-accrual		26,812	6,510
90 Days or More Past Due, Still Accruing Interest		0	4,081
Commercial real estate | Multi-family
Financing Receivable, Past Due [Line Items]
Current	[1]	813,422	759,402
Total Past Due		4,022	4,783
Total Loans		817,444	764,185
Non-accrual		2,152	3,107
90 Days or More Past Due, Still Accruing Interest		0	189
Commercial real estate | Construction
Financing Receivable, Past Due [Line Items]
Current	[1]	635,270	645,774
Total Past Due		1,986	3,563
Total Loans		637,256	649,337
Non-accrual		152	144
90 Days or More Past Due, Still Accruing Interest		63	0
Commercial real estate | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Current	[1]	1,419,276	1,353,442
Total Past Due		6,016	8,368
Total Loans		1,425,292	1,361,810
Non-accrual		4,680	2,854
90 Days or More Past Due, Still Accruing Interest		1,112	2,197
Commercial real estate | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		12,781	18,036
Commercial real estate | 30-89 Days Past Due | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Total Past Due		7,289	8,209
Commercial real estate | 30-89 Days Past Due | Multi-family
Financing Receivable, Past Due [Line Items]
Total Past Due		1,870	1,487
Commercial real estate | 30-89 Days Past Due | Construction
Financing Receivable, Past Due [Line Items]
Total Past Due		1,771	3,419
Commercial real estate | 30-89 Days Past Due | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Total Past Due		1,851	4,921
Commercial real estate | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		22,304	16,536
Commercial real estate | 90 Days or More Past Due | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Total Past Due		15,772	9,649
Commercial real estate | 90 Days or More Past Due | Multi-family
Financing Receivable, Past Due [Line Items]
Total Past Due		2,152	3,296
Commercial real estate | 90 Days or More Past Due | Construction
Financing Receivable, Past Due [Line Items]
Total Past Due		215	144
Commercial real estate | 90 Days or More Past Due | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Total Past Due		4,165	3,447
Total corporate loans
Financing Receivable, Past Due [Line Items]
Current	[1]	9,679,751	9,075,198
Total Past Due		81,219	72,272
Total Loans		9,760,970	9,147,470
Non-accrual		66,777	47,686
90 Days or More Past Due, Still Accruing Interest		3,180	6,990
Total corporate loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		40,676	27,808
Total corporate loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		40,543	44,464
Consumer loans
Financing Receivable, Past Due [Line Items]
Current	[1]	2,992,061	2,281,978
Total Past Due		20,288	17,335
Total Loans		3,012,349	2,299,313
Non-accrual		10,915	9,249
90 Days or More Past Due, Still Accruing Interest		1,477	1,292
Consumer loans | Home equity
Financing Receivable, Past Due [Line Items]
Current	[1]	823,373	843,217
Total Past Due		10,582	8,390
Total Loans		833,955	851,607
Non-accrual		7,326	5,393
90 Days or More Past Due, Still Accruing Interest		175	104
Consumer loans | 1-4 family mortgages
Financing Receivable, Past Due [Line Items]
Current	[1]	1,680,096	1,009,925
Total Past Due		6,871	7,256
Total Loans		1,686,967	1,017,181
Non-accrual		3,589	3,856
90 Days or More Past Due, Still Accruing Interest		0	1,147
Consumer loans | Installment
Financing Receivable, Past Due [Line Items]
Current	[1]	488,592	428,836
Total Past Due		2,835	1,689
Total Loans		491,427	430,525
Non-accrual		0	0
90 Days or More Past Due, Still Accruing Interest		1,302	41
Consumer loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		13,198	12,294
Consumer loans | 30-89 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Total Past Due		6,373	6,285
Consumer loans | 30-89 Days Past Due | 1-4 family mortgages
Financing Receivable, Past Due [Line Items]
Total Past Due		5,292	4,361
Consumer loans | 30-89 Days Past Due | Installment
Financing Receivable, Past Due [Line Items]
Total Past Due		1,533	1,648
Consumer loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		7,090	5,041
Consumer loans | 90 Days or More Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Total Past Due		4,209	2,105
Consumer loans | 90 Days or More Past Due | 1-4 family mortgages
Financing Receivable, Past Due [Line Items]
Total Past Due		1,579	2,895
Consumer loans | 90 Days or More Past Due | Installment
Financing Receivable, Past Due [Line Items]
Total Past Due		$ 1,302	$ 41

[1] PCI loans with an accretable yield are considered current.