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		Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Current	[1]	$ 12,435,186	$ 11,357,176
Total Past Due		84,418	89,607
Total Loans		12,519,604	11,446,783
Non-accrual		63,477	56,935
90 Days or More Past Due, Still Accruing Interest		2,615	8,282
30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		44,339	40,102
90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		40,079	49,505
Commercial, Industrial, and Agricultural
Financing Receivable, Past Due [Line Items]
Total Loans		4,954,990	4,551,221
Commercial, Industrial, and Agricultural | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Current	[1]	4,499,340	4,085,164
Total Past Due		25,061	35,129
Total Loans		4,524,401	4,120,293
Non-accrual		19,809	33,507
90 Days or More Past Due, Still Accruing Interest		1,469	422
Commercial, Industrial, and Agricultural | Agricultural
Financing Receivable, Past Due [Line Items]
Current	[1]	423,157	428,357
Total Past Due		7,432	2,571
Total Loans		430,589	430,928
Non-accrual		6,712	1,564
90 Days or More Past Due, Still Accruing Interest		0	101
Commercial, Industrial, and Agricultural | 30-89 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Past Due		15,147	8,832
Commercial, Industrial, and Agricultural | 30-89 Days Past Due | Agricultural
Financing Receivable, Past Due [Line Items]
Total Past Due		5,561	940
Commercial, Industrial, and Agricultural | 90 Days or More Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Past Due		9,914	26,297
Commercial, Industrial, and Agricultural | 90 Days or More Past Due | Agricultural
Financing Receivable, Past Due [Line Items]
Total Past Due		1,871	1,631
Commercial real estate
Financing Receivable, Past Due [Line Items]
Current	[1]	4,789,121	4,561,677
Total Past Due		36,891	34,572
Total Loans		4,826,012	4,596,249
Non-accrual		27,331	12,615
90 Days or More Past Due, Still Accruing Interest		250	6,467
Commercial real estate | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Current	[1]	1,917,718	1,803,059
Total Past Due		18,859	17,858
Total Loans		1,936,577	1,820,917
Non-accrual		17,875	6,510
90 Days or More Past Due, Still Accruing Interest		152	4,081
Commercial real estate | Multi-family
Financing Receivable, Past Due [Line Items]
Current	[1]	781,811	759,402
Total Past Due		5,344	4,783
Total Loans		787,155	764,185
Non-accrual		5,322	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]	651,343	645,774
Total Past Due		3,264	3,563
Total Loans		654,607	649,337
Non-accrual		152	144
90 Days or More Past Due, Still Accruing Interest		0	0
Commercial real estate | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Current	[1]	1,438,249	1,353,442
Total Past Due		9,424	8,368
Total Loans		1,447,673	1,361,810
Non-accrual		3,982	2,854
90 Days or More Past Due, Still Accruing Interest		98	2,197
Commercial real estate | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		13,679	18,036
Commercial real estate | 30-89 Days Past Due | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Total Past Due		2,323	8,209
Commercial real estate | 30-89 Days Past Due | Multi-family
Financing Receivable, Past Due [Line Items]
Total Past Due		404	1,487
Commercial real estate | 30-89 Days Past Due | Construction
Financing Receivable, Past Due [Line Items]
Total Past Due		3,112	3,419
Commercial real estate | 30-89 Days Past Due | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Total Past Due		7,840	4,921
Commercial real estate | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		23,212	16,536
Commercial real estate | 90 Days or More Past Due | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Total Past Due		16,536	9,649
Commercial real estate | 90 Days or More Past Due | Multi-family
Financing Receivable, Past Due [Line Items]
Total Past Due		4,940	3,296
Commercial real estate | 90 Days or More Past Due | Construction
Financing Receivable, Past Due [Line Items]
Total Past Due		152	144
Commercial real estate | 90 Days or More Past Due | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Total Past Due		1,584	3,447
Total corporate loans
Financing Receivable, Past Due [Line Items]
Current	[1]	9,711,618	9,075,198
Total Past Due		69,384	72,272
Total Loans		9,781,002	9,147,470
Non-accrual		53,852	47,686
90 Days or More Past Due, Still Accruing Interest		1,719	6,990
Total corporate loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		34,387	27,808
Total corporate loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		34,997	44,464
Consumer loans
Financing Receivable, Past Due [Line Items]
Current	[1]	2,723,568	2,281,978
Total Past Due		15,034	17,335
Total Loans		2,738,602	2,299,313
Non-accrual		9,625	9,249
90 Days or More Past Due, Still Accruing Interest		896	1,292
Consumer loans | Home equity
Financing Receivable, Past Due [Line Items]
Current	[1]	866,924	843,217
Total Past Due		7,762	8,390
Total Loans		874,686	851,607
Non-accrual		5,839	5,393
90 Days or More Past Due, Still Accruing Interest		13	104
Consumer loans | 1-4 family mortgages
Financing Receivable, Past Due [Line Items]
Current	[1]	1,385,737	1,009,925
Total Past Due		6,077	7,256
Total Loans		1,391,814	1,017,181
Non-accrual		3,786	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]	470,907	428,836
Total Past Due		1,195	1,689
Total Loans		472,102	430,525
Non-accrual		0	0
90 Days or More Past Due, Still Accruing Interest		883	41
Consumer loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		9,952	12,294
Consumer loans | 30-89 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Total Past Due		5,243	6,285
Consumer loans | 30-89 Days Past Due | 1-4 family mortgages
Financing Receivable, Past Due [Line Items]
Total Past Due		4,397	4,361
Consumer loans | 30-89 Days Past Due | Installment
Financing Receivable, Past Due [Line Items]
Total Past Due		312	1,648
Consumer loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due		5,082	5,041
Consumer loans | 90 Days or More Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Total Past Due		2,519	2,105
Consumer loans | 90 Days or More Past Due | 1-4 family mortgages
Financing Receivable, Past Due [Line Items]
Total Past Due		1,680	2,895
Consumer loans | 90 Days or More Past Due | Installment
Financing Receivable, Past Due [Line Items]
Total Past Due		$ 883	$ 41

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