Allowance for Credit Losses and Credit Quality Information - Schedule of Commercial Credit Exposure (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	100.00%
Acquired nonimpaired loans	$ 3,221,316	$ 429,982
Total Special Mention and Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	3.00%
Acquired impaired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	0.00%
Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	97.00%
Total Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	$ 6,335,952
Acquired nonimpaired loans	2,200,000
Total Commercial | Special mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	52,765
Total Commercial | Accrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	134,505
Total Commercial | Nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	15,515
Total Commercial | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	1,202
Total Commercial | Total Special Mention and Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	203,987
Total Commercial | Acquired impaired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	17,482
Total Commercial | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	6,114,483
Total Commercial | Commercial and industrial(1)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	2,235,428
Acquired nonimpaired loans	603,157	89,970
Total Commercial | Commercial and industrial(1) | Special mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	12,287
Total Commercial | Commercial and industrial(1) | Accrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	78,809
Total Commercial | Commercial and industrial(1) | Nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	9,852
Total Commercial | Commercial and industrial(1) | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	1,179
Total Commercial | Commercial and industrial(1) | Total Special Mention and Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	102,127
Total Commercial | Commercial and industrial(1) | Acquired impaired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	1,564
Total Commercial | Commercial and industrial(1) | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	2,131,737
Total Commercial | Owner-occupied commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	1,296,466
Acquired nonimpaired loans	313,955	112,386
Total Commercial | Owner-occupied commercial | Special mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	0
Total Commercial | Owner-occupied commercial | Accrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	32,679
Total Commercial | Owner-occupied commercial | Nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	4,037
Total Commercial | Owner-occupied commercial | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	23
Total Commercial | Owner-occupied commercial | Total Special Mention and Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	36,739
Total Commercial | Owner-occupied commercial | Acquired impaired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	6,757
Total Commercial | Owner-occupied commercial | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	1,252,970
Total Commercial | Commercial mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	2,222,976
Acquired nonimpaired loans	1,107,379	145,648
Total Commercial | Commercial mortgages | Special mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	40,478
Total Commercial | Commercial mortgages | Accrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	23,017
Total Commercial | Commercial mortgages | Nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	1,626
Total Commercial | Commercial mortgages | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	0
Total Commercial | Commercial mortgages | Total Special Mention and Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	65,121
Total Commercial | Commercial mortgages | Acquired impaired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	8,670
Total Commercial | Commercial mortgages | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	2,149,185
Total Commercial | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	581,082
Acquired nonimpaired loans	142,592	$ 2,525
Total Commercial | Construction | Special mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	0
Total Commercial | Construction | Accrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	0
Total Commercial | Construction | Nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	0
Total Commercial | Construction | Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	0
Total Commercial | Construction | Total Special Mention and Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	0
Total Commercial | Construction | Acquired impaired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	491
Total Commercial | Construction | Pass
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Loans	$ 580,591