Mergers and Acquisitions - Narrative (Details)		12 Months Ended
	Nov. 12, 2021 USD ($) lease_obligation office branch $ / shares	Dec. 31, 2021 USD ($) business	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Business Acquisition [Line Items]
Total assets		$ 23,512,128,000	$ 15,964,190,000	$ 11,628,775,000
Loans, net of allowance for loan losses		12,157,281,000	9,593,958,000
Deposits		19,628,311,000	12,155,784,000
Goodwill		631,496,000	369,477,000	369,031,000
Gain (loss) on disposition of property plant equipment		(4,715,000)	(73,000)	$ (271,000)
Right-of-use asset acquired	$ 13,900,000
Lease liability acquired	13,900,000
Acquisition-related and professional fee costs		35,456,000
Century Bancorp, Inc.
Business Acquisition [Line Items]
Total assets	7,100,000,000
Loans, net of allowance for loan losses		2,900,000,000
Deposits	$ 6,100,000,000
Number of full service banking offices | office	29
Financial Asset Acquired with Credit Deterioration | Century Bancorp, Inc.
Business Acquisition [Line Items]
Loans, net of allowance for loan losses		67,300,000
Century Bancorp, Inc.
Business Acquisition [Line Items]
Share price (in dollars per share) | $ / shares	$ 115.28
Total fair value of consideration	$ 641,900,000
Deposits		472,300,000
Goodwill	259,024,000
Investment securities premium (discount) acquired	(37,300,000)
Debt discount (premium) acquired	$ 13,300,000
Number of branches acquired | branch	29
Premises and equipment	$ 64,521,000
Asset acquisition, consideration transferred	20,500,000
Gain (loss) on disposition of property plant equipment	$ 0
Number of lease obligations | lease_obligation	20
Core deposit intangible	$ 11,633,000
Business acquisition, goodwill, expected tax deductible amount	0
Bank owned life insurance	95,478,000
Time deposits	1,800,000
Securities sold under agreements to repurchase	274,982,000
Escrow deposit	3,600,000
Acquisition-related and professional fee costs		35,500,000
Century Bancorp, Inc. | Core deposits
Business Acquisition [Line Items]
Core deposit intangible	$ 11,600,000
Weighted average useful life acquired	10 years
Insurance Agency Acquisition
Business Acquisition [Line Items]
Total fair value of consideration		5,158,000	1,656,000
Goodwill		$ 2,995,000	446,000
Number of businesses acquired | business		2
Total cash paid		$ 4,354,000	1,363,000
Contingent consideration		400,000	300,000
Contingent consideration liability, payouts, low		0	0
Contingent consideration liability, payouts, high		500,000	300,000
Merger and acquisition expenses		100,000	$ 100,000
Insurance Agency Acquisition One
Business Acquisition [Line Items]
Total cash paid		3,900,000
Insurance Agency Acquisition Two
Business Acquisition [Line Items]
Total cash paid		$ 500,000