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Mergers and Acquisitions - Summary of Purchase Price Consideration (Details) - Sterling - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	9 Months Ended
	Jan. 31, 2022	Sep. 30, 2022	Sep. 30, 2022	Sep. 30, 2021
Business Acquisition [Line Items]
Webster common stock issued (in shares)	87,965,239
Price per share of Webster common stock on January 31, 2022 (in dollars per share)	$ 56.81
Total consideration	$ 5,180,300
Common Stock
Business Acquisition [Line Items]
Total consideration	4,997,305
Preferred Stock
Business Acquisition [Line Items]
Total consideration	138,942		$ 138,942	$ 0
Replacement Equity Awards
Business Acquisition [Line Items]
Total consideration	43,877
Stock compensation expense		$ 2,600	$ 16,400
Fractional Shares
Business Acquisition [Line Items]
Total consideration	$ 176