Past Due Loans, Allowance For Credit Losses, Non-Accrual Loans, and TDRS - Corporate Loans Portfolio Segment By Origination Year (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving loans converted to term loans	$ 16,800	$ 23,800
Corporate Loan | Commercial Industrial And Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
2020	465,536	465,536
2019	899,959	899,959
2018	985,321	985,321
2017	550,918	550,918
2016	268,667	268,667
Prior	509,496	509,496
Revolving Loans	1,490,783	1,490,783
Total	5,170,680	5,170,680
Corporate Loan | Commercial Industrial And Agricultural | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	461,644	461,644
2019	887,292	887,292
2018	924,776	924,776
2017	519,875	519,875
2016	238,751	238,751
Prior	469,442	469,442
Revolving Loans	1,364,316	1,364,316
Total	4,866,096	4,866,096
Corporate Loan | Commercial Industrial And Agricultural | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,508	3,508
2019	6,520	6,520
2018	31,435	31,435
2017	4,676	4,676
2016	8,527	8,527
Prior	17,568	17,568
Revolving Loans	80,597	80,597
Total	152,831	152,831
Corporate Loan | Commercial Industrial And Agricultural | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	384	384
2019	4,376	4,376
2018	26,729	26,729
2017	17,862	17,862
2016	16,583	16,583
Prior	15,804	15,804
Revolving Loans	33,172	33,172
Total	114,910	114,910
Corporate Loan | Commercial Industrial And Agricultural | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	1,771	1,771
2018	2,381	2,381
2017	8,505	8,505
2016	4,806	4,806
Prior	6,682	6,682
Revolving Loans	12,698	12,698
Total	36,843	36,843
Corporate Loan | Commercial Industrial And Agricultural | Net Loan Charge Offs
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	250	250
2018	946	946
2017	1,058	1,058
2016	617	617
Prior	1,853	1,853
Revolving Loans	6,036	6,036
Total	10,760	10,760
Corporate Loan | Office, retail, and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	96,464	96,464
2019	267,134	267,134
2018	229,350	229,350
2017	353,549	353,549
2016	329,621	329,621
Prior	738,709	738,709
Revolving Loans	5,491	5,491
Total	2,020,318	2,020,318
Corporate Loan | Office, retail, and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	95,291	95,291
2019	266,479	266,479
2018	225,938	225,938
2017	348,121	348,121
2016	302,430	302,430
Prior	677,880	677,880
Revolving Loans	5,491	5,491
Total	1,921,630	1,921,630
Corporate Loan | Office, retail, and industrial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,173	1,173
2019	655	655
2018	3,280	3,280
2017	5,091	5,091
2016	15,439	15,439
Prior	12,914	12,914
Revolving Loans	0	0
Total	38,552	38,552
Corporate Loan | Office, retail, and industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	0	0
2018	0	0
2017	337	337
2016	1,514	1,514
Prior	22,370	22,370
Revolving Loans	0	0
Total	24,221	24,221
Corporate Loan | Office, retail, and industrial | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	0	0
2018	132	132
2017	0	0
2016	10,238	10,238
Prior	25,545	25,545
Revolving Loans	0	0
Total	35,915	35,915
Corporate Loan | Office, retail, and industrial | Net Loan Charge Offs
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	333	333
2018	156	156
2017	0	0
2016	1,628	1,628
Prior	1,298	1,298
Revolving Loans	0	0
Total	3,415	3,415
Corporate Loan | Multi-family
Financing Receivable, Credit Quality Indicator [Line Items]
2020	125,328	125,328
2019	174,802	174,802
2018	85,178	85,178
2017	103,358	103,358
2016	102,441	102,441
Prior	247,643	247,643
Revolving Loans	36,111	36,111
Total	874,861	874,861
Corporate Loan | Multi-family | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	125,328	125,328
2019	174,802	174,802
2018	84,791	84,791
2017	101,492	101,492
2016	101,846	101,846
Prior	239,713	239,713
Revolving Loans	36,111	36,111
Total	864,083	864,083
Corporate Loan | Multi-family | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	0	0
2018	0	0
2017	0	0
2016	358	358
Prior	1,416	1,416
Revolving Loans	0	0
Total	1,774	1,774
Corporate Loan | Multi-family | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	0	0
2018	387	387
2017	81	81
2016	0	0
Prior	5,415	5,415
Revolving Loans	0	0
Total	5,883	5,883
Corporate Loan | Multi-family | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	0	0
2018	0	0
2017	1,785	1,785
2016	237	237
Prior	1,099	1,099
Revolving Loans	0	0
Total	3,121	3,121
Corporate Loan | Multi-family | Net Loan Charge Offs
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	3	3
2018	0	0
2017	1	1
2016	0	0
Prior	10	10
Revolving Loans	0	0
Total	14	14
Corporate Loan | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	33,890	33,890
2019	151,849	151,849
2018	171,525	171,525
2017	104,813	104,813
2016	85,222	85,222
Prior	105,057	105,057
Revolving Loans	34,707	34,707
Total	687,063	687,063
Corporate Loan | Construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	33,890	33,890
2019	151,849	151,849
2018	171,480	171,480
2017	101,781	101,781
2016	71,001	71,001
Prior	70,950	70,950
Revolving Loans	33,016	33,016
Total	633,967	633,967
Corporate Loan | Construction | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	0	0
2018	45	45
2017	3,032	3,032
2016	14,221	14,221
Prior	1,228	1,228
Revolving Loans	0	0
Total	18,526	18,526
Corporate Loan | Construction | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	0	0
2018	0	0
2017	0	0
2016	0	0
Prior	7,288	7,288
Revolving Loans	0	0
Total	7,288	7,288
Corporate Loan | Construction | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	0	0
2018	0	0
2017	0	0
2016	0	0
Prior	25,591	25,591
Revolving Loans	1,691	1,691
Total	27,282	27,282
Corporate Loan | Construction | Net Loan Charge Offs
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	118	118
2018	0	0
2017	798	798
2016	0	0
Prior	1,690	1,690
Revolving Loans	0	0
Total	2,606	2,606
Corporate Loan | Other commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	61,056	61,056
2019	199,300	199,300
2018	277,789	277,789
2017	238,501	238,501
2016	141,770	141,770
Prior	529,875	529,875
Revolving Loans	27,646	27,646
Total	1,475,937	1,475,937
Corporate Loan | Other commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	61,056	61,056
2019	195,768	195,768
2018	269,526	269,526
2017	226,064	226,064
2016	125,249	125,249
Prior	466,436	466,436
Revolving Loans	27,553	27,553
Total	1,371,652	1,371,652
Corporate Loan | Other commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	3,532	3,532
2018	7,589	7,589
2017	6,887	6,887
2016	11,219	11,219
Prior	15,463	15,463
Revolving Loans	0	0
Total	44,690	44,690
Corporate Loan | Other commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	0	0
2018	0	0
2017	1,400	1,400
2016	4,224	4,224
Prior	35,599	35,599
Revolving Loans	0	0
Total	41,223	41,223
Corporate Loan | Other commercial real estate | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	0	0
2018	674	674
2017	4,150	4,150
2016	1,078	1,078
Prior	12,377	12,377
Revolving Loans	93	93
Total	18,372	18,372
Corporate Loan | Other commercial real estate | Net Loan Charge Offs
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	38	38
2018	1	1
2017	0	0
2016	183	183
Prior	(39)	(39)
Revolving Loans	0	0
Total	183	183
Consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total			$ 3,271,117
Consumer loans | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
2020	8,231	8,231
2019	48,718	48,718
2018	27,908	27,908
2017	14,073	14,073
2016	12,360	12,360
Prior	63,854	63,854
Revolving Loans	717,723	717,723
Total	892,867	892,867	851,454
Consumer loans | Home equity | Performing Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	8,231	8,231
2019	48,696	48,696
2018	27,783	27,783
2017	13,809	13,809
2016	11,878	11,878
Prior	57,053	57,053
Revolving Loans	716,288	716,288
Total	883,738	883,738
Consumer loans | Home equity | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	22	22
2018	125	125
2017	264	264
2016	482	482
Prior	6,801	6,801
Revolving Loans	1,435	1,435
Total	9,129	9,129
Consumer loans | Home equity | Net Loan Charge Offs
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	0	0
2018	1	1
2017	0	0
2016	1	1
Prior	42	42
Revolving Loans	(14)	(14)
Total	30	30
Consumer loans | 1-4 Family Mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
2020	597,506	597,506
2019	676,898	676,898
2018	312,322	312,322
2017	158,313	158,313
2016	181,975	181,975
Prior	248,308	248,308
Revolving Loans	0	0
Total	2,175,322	2,175,322
Consumer loans | 1-4 Family Mortgages | Performing Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	597,506	597,506
2019	676,898	676,898
2018	311,884	311,884
2017	158,230	158,230
2016	181,912	181,912
Prior	240,394	240,394
Revolving Loans	0	0
Total	2,166,824	2,166,824
Consumer loans | 1-4 Family Mortgages | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	0	0
2018	438	438
2017	83	83
2016	63	63
Prior	7,914	7,914
Revolving Loans	0	0
Total	8,498	8,498
Consumer loans | 1-4 Family Mortgages | Net Loan Charge Offs
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	0	0
2018	4	4
2017	0	0
2016	7	7
Prior	735	735
Revolving Loans	0	0
Total	746	746
Consumer loans | Installment
Financing Receivable, Credit Quality Indicator [Line Items]
2020	59,971	59,971
2019	185,919	185,919
2018	107,220	107,220
2017	45,108	45,108
2016	17,563	17,563
Prior	20,662	20,662
Revolving Loans	20,764	20,764
Total	457,207	457,207	$ 492,585
Consumer loans | Installment | Performing Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	59,971	59,971
2019	185,919	185,919
2018	107,220	107,220
2017	45,108	45,108
2016	17,563	17,563
Prior	20,662	20,662
Revolving Loans	20,764	20,764
Total	457,207	457,207
Consumer loans | Installment | Non-accrual
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0	0
2019	0	0
2018	0	0
2017	0	0
2016	0	0
Prior	0	0
Revolving Loans	0	0
Total	0	0
Consumer loans | Installment | Net Loan Charge Offs
Financing Receivable, Credit Quality Indicator [Line Items]
2020	44	44
2019	3,757	3,757
2018	2,200	2,200
2017	775	775
2016	85	85
Prior	393	393
Revolving Loans	29	29
Total	$ 7,283	$ 7,283