Allowance for Credit Losses - Loan Balances by Year of Origination and Performing and Nonperforming Status (Details) - USD ($) $ in Thousands	Jun. 30, 2020		Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 1,004,189
2019	1,260,757
2018	963,963
2017	665,166
2016	701,082
2015 and Prior	1,885,082
Revolving	1,059,103
Revolving-Term	9,216
Total	7,548,558	[1]	$ 7,137,152
Performing
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,004,189
2019	1,259,835
2018	960,948
2017	661,501
2016	678,413
2015 and Prior	1,831,427
Revolving	1,053,073
Revolving-Term	9,059
Total	7,458,445
Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	922
2018	3,015
2017	3,665
2016	22,668
2015 and Prior	53,655
Revolving	6,030
Revolving-Term	157
Total	90,113
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	231,670
2019	477,527
2018	444,368
2017	350,151
2016	431,828
2015 and Prior	872,712
Revolving	53,847
Revolving-Term	0
Total	2,862,103
Commercial real estate | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
2020	231,670
2019	477,527
2018	444,368
2017	350,151
2016	411,792
2015 and Prior	839,942
Revolving	50,877
Revolving-Term	0
Total	2,806,327
Commercial real estate | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	20,036
2015 and Prior	32,770
Revolving	2,970
Revolving-Term	0
Total	55,776
Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	351,004
2019	243,588
2018	169,080
2017	104,375
2016	63,338
2015 and Prior	322,811
Revolving	428,436
Revolving-Term	44
Total	1,682,676
Commercial and industrial | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
2020	351,004
2019	243,588
2018	168,814
2017	104,375
2016	63,338
2015 and Prior	322,811
Revolving	426,076
Revolving-Term	44
Total	1,680,050
Commercial and industrial | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	266
2017	0
2016	0
2015 and Prior	0
Revolving	2,360
Revolving-Term	0
Total	2,626
Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	67,685
2019	206,187
2018	111,508
2017	19,241
2016	17,335
2015 and Prior	19,207
Revolving	11,935
Revolving-Term	0
Total	453,098
Commercial construction | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
2020	67,685
2019	206,187
2018	111,508
2017	18,200
2016	17,335
2015 and Prior	18,744
Revolving	11,935
Revolving-Term	0
Total	451,594
Commercial construction | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	1,041
2016	0
2015 and Prior	463
Revolving	0
Revolving-Term	0
Total	1,504
Business banking
Financing Receivable, Credit Quality Indicator [Line Items]
2020	289,837
2019	172,630
2018	147,368
2017	105,944
2016	94,054
2015 and Prior	345,569
Revolving	111,911
Revolving-Term	1,522
Total	1,268,835
Business banking | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
2020	289,837
2019	172,290
2018	145,563
2017	104,549
2016	92,708
2015 and Prior	334,316
Revolving	111,696
Revolving-Term	1,401
Total	1,252,360
Business banking | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	340
2018	1,805
2017	1,395
2016	1,346
2015 and Prior	11,253
Revolving	215
Revolving-Term	121
Total	16,475
Consumer real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	59,273
2019	143,279
2018	82,271
2017	80,015
2016	89,580
2015 and Prior	318,383
Revolving	422,189
Revolving-Term	7,123
Total	1,202,113
Consumer real estate | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
2020	59,273
2019	143,174
2018	81,327
2017	78,888
2016	88,576
2015 and Prior	309,984
Revolving	421,895
Revolving-Term	7,123
Total	1,190,240
Consumer real estate | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	105
2018	944
2017	1,127
2016	1,004
2015 and Prior	8,399
Revolving	294
Revolving-Term	0
Total	11,873
Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2020	4,720
2019	17,546
2018	9,368
2017	5,440
2016	4,947
2015 and Prior	6,400
Revolving	30,785
Revolving-Term	527
Total	79,733
Other consumer | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
2020	4,720
2019	17,069
2018	9,368
2017	5,338
2016	4,664
2015 and Prior	5,630
Revolving	30,594
Revolving-Term	491
Total	77,874
Other consumer | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	477
2018	0
2017	102
2016	283
2015 and Prior	770
Revolving	191
Revolving-Term	36
Total	$ 1,859

[1] We had 2,360 loans that were modified totaling $1.4 billion under the CARES Act at June 30, 2020. These customers were not considered past due as a result of their delayed payments. Upon exiting the loan modification deferral program, the measurement of loan delinquency will resume where it left off upon entry into the program. Due to the modification program, this delinquency table may not accurately reflect the credit risk associated with these loans.