Junior Subordinated Debentures - Schedule of Junior Subordinated Debentures (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2025	Dec. 31, 2024	Sep. 30, 2024
Subordinated Borrowing [Line Items]
Junior Subordinated Debentures	$ 253,566	$ 253,566	$ 253,566
Junior Subordinated Debt
Subordinated Borrowing [Line Items]
Junior Subordinated Debentures	$ 253,566	$ 253,600	$ 253,600
Weighted average contractual rate	6.52%
Junior Subordinated Debt | Wintrust Capital Trust III
Subordinated Borrowing [Line Items]
Common Securities	$ 774
Trust  Preferred Securities	25,000
Junior Subordinated Debentures	$ 25,774
Rate structure, stated	0.26161%
Rate structure, variable	3.25%
Weighted average contractual rate	7.83%
Junior Subordinated Debt | Wintrust Statutory Trust IV
Subordinated Borrowing [Line Items]
Common Securities	$ 619
Trust  Preferred Securities	20,000
Junior Subordinated Debentures	$ 20,619
Rate structure, stated	0.26161%
Rate structure, variable	2.80%
Weighted average contractual rate	7.06%
Junior Subordinated Debt | Wintrust Statutory Trust V
Subordinated Borrowing [Line Items]
Common Securities	$ 1,238
Trust  Preferred Securities	40,000
Junior Subordinated Debentures	$ 41,238
Rate structure, stated	0.26161%
Rate structure, variable	2.60%
Weighted average contractual rate	6.86%
Junior Subordinated Debt | Wintrust Capital Trust VII
Subordinated Borrowing [Line Items]
Common Securities	$ 1,550
Trust  Preferred Securities	50,000
Junior Subordinated Debentures	$ 51,550
Rate structure, stated	0.26161%
Rate structure, variable	1.95%
Weighted average contractual rate	6.25%
Junior Subordinated Debt | Wintrust Capital Trust VIII
Subordinated Borrowing [Line Items]
Common Securities	$ 1,238
Trust  Preferred Securities	25,000
Junior Subordinated Debentures	$ 26,238
Rate structure, stated	0.26161%
Rate structure, variable	1.45%
Weighted average contractual rate	5.71%
Junior Subordinated Debt | Wintrust Capital Trust IX
Subordinated Borrowing [Line Items]
Common Securities	$ 1,547
Trust  Preferred Securities	50,000
Junior Subordinated Debentures	$ 51,547
Rate structure, stated	0.26161%
Rate structure, variable	1.63%
Weighted average contractual rate	5.93%
Junior Subordinated Debt | Northview Capital Trust I
Subordinated Borrowing [Line Items]
Common Securities	$ 186
Trust  Preferred Securities	6,000
Junior Subordinated Debentures	$ 6,186
Rate structure, stated	0.26161%
Rate structure, variable	3.00%
Weighted average contractual rate	7.56%
Junior Subordinated Debt | Town Bankshares Capital Trust I
Subordinated Borrowing [Line Items]
Common Securities	$ 186
Trust  Preferred Securities	6,000
Junior Subordinated Debentures	$ 6,186
Rate structure, stated	0.26161%
Rate structure, variable	3.00%
Weighted average contractual rate	7.56%
Junior Subordinated Debt | First Northwest Capital Trust I
Subordinated Borrowing [Line Items]
Common Securities	$ 155
Trust  Preferred Securities	5,000
Junior Subordinated Debentures	$ 5,155
Rate structure, stated	0.26161%
Rate structure, variable	3.00%
Weighted average contractual rate	7.26%
Junior Subordinated Debt | Suburban Illinois Capital Trust II
Subordinated Borrowing [Line Items]
Common Securities	$ 464
Trust  Preferred Securities	15,000
Junior Subordinated Debentures	$ 15,464
Rate structure, stated	0.26161%
Rate structure, variable	1.75%
Weighted average contractual rate	6.05%
Junior Subordinated Debt | Community Financial Shares Statutory Trust II
Subordinated Borrowing [Line Items]
Common Securities	$ 109
Trust  Preferred Securities	3,500
Junior Subordinated Debentures	$ 3,609
Rate structure, stated	0.26161%
Rate structure, variable	1.62%
Weighted average contractual rate	5.92%