Allowance for Credit Losses - Amortized Cost Basis by Year of Origination and Credit Quality Indicator (Details) $ in Thousands	Mar. 31, 2020 USD ($)
Residential and consumer
Credit quality
2020	$ 520,211
2019	2,312,205
2018	1,969,068
2017	1,533,858
2016	1,036,924
Prior	2,827,658
Revolving Loans Amortized Cost Basis	3,116,593
Revolving Loans Converted to Term Loans Amortized Cost Basis	63,753
Total	13,380,270
Residential
Credit quality
2020	185,155
2019	559,632
2018	518,792
2017	577,924
2016	465,819
Prior	1,365,048
Revolving Loans Amortized Cost Basis	892,278
Revolving Loans Converted to Term Loans Amortized Cost Basis	505
Total	4,565,153
Consumer
Credit quality
2020	92,841
2019	392,843
2018	315,807
2017	206,199
2016	107,376
Prior	55,828
Revolving Loans Amortized Cost Basis	397,179
Total	1,568,073
Consumer | 740 and greater
Credit quality
2020	46,781
2019	150,459
2018	128,010
2017	76,608
2016	41,303
Prior	17,034
Revolving Loans Amortized Cost Basis	117,149
Total	577,344
Consumer | 680 - 739
Credit quality
2020	29,047
2019	124,783
2018	99,908
2017	59,075
2016	29,503
Prior	13,332
Revolving Loans Amortized Cost Basis	92,315
Total	447,963
Consumer | 620 - 679
Credit quality
2020	11,357
2019	73,221
2018	51,785
2017	35,102
2016	18,932
Prior	9,072
Revolving Loans Amortized Cost Basis	49,123
Total	248,592
Consumer | 550 - 619
Credit quality
2020	1,679
2019	21,334
2018	23,130
2017	20,105
2016	10,676
Prior	6,105
Revolving Loans Amortized Cost Basis	18,624
Total	101,653
Consumer | Less than 550
Credit quality
2020	581
2019	7,625
2018	12,696
2017	12,928
2016	6,832
Prior	3,459
Revolving Loans Amortized Cost Basis	7,906
Total	52,027
Consumer | No Score
Credit quality
2020	2,796
2019	6,248
2018	174
2017	151
2016	30
Prior	3
Revolving Loans Amortized Cost Basis	37,382
Total	46,784
Consumer | Other
Credit quality
2020	600
2019	9,173
2018	104
2017	2,230
2016	100
Prior	6,823
Revolving Loans Amortized Cost Basis	74,680
Total	93,710
Home equity line
Credit quality
Revolving Loans Amortized Cost Basis	891,698
Total	891,698
Home equity line | 740 and greater
Credit quality
Revolving Loans Amortized Cost Basis	629,818
Total	629,818
Home equity line | 680 - 739
Credit quality
Revolving Loans Amortized Cost Basis	173,990
Total	173,990
Home equity line | 620 - 679
Credit quality
Revolving Loans Amortized Cost Basis	58,863
Total	58,863
Home equity line | 550 - 619
Credit quality
Revolving Loans Amortized Cost Basis	16,863
Total	16,863
Home equity line | Less than 550
Credit quality
Revolving Loans Amortized Cost Basis	6,852
Total	6,852
Home equity line | No Score
Credit quality
Revolving Loans Amortized Cost Basis	5,312
Total	5,312
Commercial and Industrial
Credit quality
2020	104,018
2019	393,542
2018	314,725
2017	97,907
2016	77,134
Prior	224,507
Revolving Loans Amortized Cost Basis	1,750,266
Revolving Loans Converted to Term Loans Amortized Cost Basis	63,246
Total	3,025,345
Commercial and Industrial | Pass
Credit quality
2020	96,493
2019	364,221
2018	294,506
2017	86,993
2016	72,683
Prior	210,731
Revolving Loans Amortized Cost Basis	1,542,232
Revolving Loans Converted to Term Loans Amortized Cost Basis	62,021
Total	2,729,880
Commercial and Industrial | Special mention
Credit quality
2020	126
2019	3,490
2018	2,757
2017	360
2016	535
Prior	7,064
Revolving Loans Amortized Cost Basis	88,787
Revolving Loans Converted to Term Loans Amortized Cost Basis	256
Total	103,375
Commercial and Industrial | Substandard
Credit quality
2020	160
2019	7,456
2018	3,568
2017	1,569
2016	57
Prior	5,465
Revolving Loans Amortized Cost Basis	50,830
Revolving Loans Converted to Term Loans Amortized Cost Basis	969
Total	70,074
Commercial and Industrial | Other
Credit quality
2020	7,239
2019	18,375
2018	13,894
2017	8,985
2016	3,859
Prior	1,247
Revolving Loans Amortized Cost Basis	68,417
Total	122,016
Commercial real estate
Credit quality
2020	70,775
2019	765,094
2018	594,895
2017	521,137
2016	353,770
Prior	1,056,662
Revolving Loans Amortized Cost Basis	50,679
Revolving Loans Converted to Term Loans Amortized Cost Basis	2
Total	3,413,014
Commercial real estate | Pass
Credit quality
2020	70,775
2019	731,880
2018	577,488
2017	497,579
2016	324,782
Prior	1,024,477
Revolving Loans Amortized Cost Basis	47,680
Revolving Loans Converted to Term Loans Amortized Cost Basis	2
Total	3,274,663
Commercial real estate | Special mention
Credit quality
2019	8,810
2018	17,407
2017	23,558
2016	28,562
Prior	27,346
Revolving Loans Amortized Cost Basis	2,999
Total	108,682
Commercial real estate | Substandard
Credit quality
2019	24,404
2016	426
Prior	4,325
Total	29,155
Commercial real estate | Other
Credit quality
Prior	514
Total	514
Construction
Credit quality
2020	17,806
2019	127,741
2018	206,767
2017	107,988
2016	26,886
Prior	58,683
Revolving Loans Amortized Cost Basis	26,191
Total	572,062
Construction | Pass
Credit quality
2020	15,537
2019	96,333
2018	192,397
2017	99,207
2016	25,151
Prior	53,105
Revolving Loans Amortized Cost Basis	25,991
Total	507,721
Construction | Special mention
Credit quality
Revolving Loans Amortized Cost Basis	200
Total	200
Construction | Substandard
Credit quality
2017	2,219
Prior	1,002
Total	3,221
Construction | Other
Credit quality
2020	2,269
2019	31,408
2018	14,370
2017	6,562
2016	1,735
Prior	4,576
Total	60,920
Lease financing
Credit quality
2020	49,616
2019	73,353
2018	18,082
2017	22,703
2016	5,939
Prior	66,930
Total	236,623
Lease financing | Pass
Credit quality
2020	49,616
2019	73,066
2018	17,998
2017	22,263
2016	5,939
Prior	66,866
Total	235,748
Lease financing | Special mention
Credit quality
2019	287
2018	84
2017	440
Prior	64
Total	875
Commercial Lending
Credit quality
2020	242,215
2019	1,359,730
2018	1,134,469
2017	749,735
2016	463,729
Prior	1,406,782
Revolving Loans Amortized Cost Basis	1,827,136
Revolving Loans Converted to Term Loans Amortized Cost Basis	63,248
Total	7,247,044
Residential mortgage
Credit quality
2020	185,155
2019	559,632
2018	518,792
2017	577,924
2016	465,819
Prior	1,365,048
Revolving Loans Amortized Cost Basis	580
Revolving Loans Converted to Term Loans Amortized Cost Basis	505
Total	3,673,455
Residential mortgage | 740 and greater
Credit quality
2020	134,802
2019	429,854
2018	380,979
2017	437,915
2016	376,570
Prior	1,044,890
Total	2,805,010
Residential mortgage | 680 - 739
Credit quality
2020	28,248
2019	71,374
2018	69,543
2017	69,434
2016	44,492
Prior	170,974
Total	454,065
Residential mortgage | 620 - 679
Credit quality
2020	3,527
2019	13,645
2018	11,235
2017	13,074
2016	11,621
Prior	57,611
Total	110,713
Residential mortgage | 550 - 619
Credit quality
2020	2,012
2019	1,834
2018	3,547
2017	4,096
2016	3,050
Prior	13,474
Total	28,013
Residential mortgage | Less than 550
Credit quality
2018	1,206
2017	1,912
2016	966
Prior	6,363
Total	10,447
Residential mortgage | No Score
Credit quality
2020	11,783
2019	21,987
2018	25,655
2017	26,042
2016	16,592
Prior	54,212
Total	156,271
Residential mortgage | Other
Credit quality
2020	4,783
2019	20,938
2018	26,627
2017	25,451
2016	12,528
Prior	17,524
Revolving Loans Amortized Cost Basis	580
Revolving Loans Converted to Term Loans Amortized Cost Basis	505
Total	$ 108,936