Merger, Acquisition, and Divestiture Activity - Total Consideration (Details) - USD ($) $ / shares in Units, shares in Thousands		12 Months Ended
	Feb. 15, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Assets
Goodwill		$ 1,998,716,000	$ 1,998,716,000	$ 1,036,994,000	$ 1,036,994,000
Fair value of consideration
Issuance of common stock			2,446,312,000
Common Stock
Fair value of consideration
Issuance of common stock		$ 129,365,000	$ 129,365,000
Share price (in dollars per share)		$ 18.92
First Midwest
Assets
Cash and cash equivalents	$ 1,912,629,000
Investment securities	3,526,278,000
FHLB/Federal Reserve Bank stock	106,097,000
Loans held-for-sale	13,809,000
Loans, net of allowance for credit losses	14,298,873,000
Premises and equipment	111,867,000
Operating lease right-of-use assets	129,698,000
Accrued interest receivable	53,502,000
Goodwill	961,722,000
Other intangible assets	117,584,000
Company-owned life insurance	301,025,000
Other assets	317,258,000
Total assets	21,850,342,000
Liabilities
Deposits	17,249,404,000
Securities sold under agreements to repurchase	135,194,000
Federal Home Loan Bank advances	1,158,623,000
Other borrowings	274,569,000
Accrued expenses and other liabilities	342,369,000
Total liabilities	19,160,159,000
Fair value of consideration
Total consideration	$ 2,690,182,000
First Midwest | Preferred Stock
Fair value of consideration
Issuance of common stock shares for acquisitions of business (in shares)	243,870
First Midwest | Common Stock
Fair value of consideration
Issuance of common stock shares for acquisitions of business (in shares)	2,446,312