Junior Subordinated Debentures (Summary of the Company's Junior Subordinated Debentures) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Subordinated Borrowing [Line Items]
Junior subordinated debentures	$ 253,566,000	$ 253,566,000
Junior Subordinated Debt
Subordinated Borrowing [Line Items]
Junior subordinated debentures	$ 253,566,000	253,566,000
Weighted average interest rate	4.94%
Junior Subordinated Debt | Wintrust Capital Trust III
Subordinated Borrowing [Line Items]
Common Securities	$ 774,000
Trust Preferred Securities	25,000,000
Junior subordinated debentures	$ 25,774,000	25,774,000
Contractual rate	5.69%
Junior Subordinated Debt | Wintrust Statutory Trust IV
Subordinated Borrowing [Line Items]
Common Securities	$ 619,000
Trust Preferred Securities	20,000,000
Junior subordinated debentures	$ 20,619,000	20,619,000
Contractual rate	5.60%
Junior Subordinated Debt | Wintrust Statutory Trust V
Subordinated Borrowing [Line Items]
Common Securities	$ 1,238,000
Trust Preferred Securities	40,000,000
Junior subordinated debentures	$ 41,238,000	41,238,000
Contractual rate	5.40%
Junior Subordinated Debt | Wintrust Capital Trust VII
Subordinated Borrowing [Line Items]
Common Securities	$ 1,550,000
Trust Preferred Securities	50,000,000
Junior subordinated debentures	$ 51,550,000	51,550,000
Contractual rate	4.74%
Junior Subordinated Debt | Wintrust Capital Trust VIII
Subordinated Borrowing [Line Items]
Common Securities	$ 1,238,000
Trust Preferred Securities	25,000,000
Junior subordinated debentures	$ 26,238,000	26,238,000
Contractual rate	4.25%
Junior Subordinated Debt | Wintrust Capital Trust IX
Subordinated Borrowing [Line Items]
Common Securities	$ 1,547,000
Trust Preferred Securities	50,000,000
Junior subordinated debentures	$ 51,547,000	51,547,000
Contractual rate	4.42%
Junior Subordinated Debt | Northview Capital Trust I
Subordinated Borrowing [Line Items]
Common Securities	$ 186,000
Trust Preferred Securities	6,000,000
Junior subordinated debentures	$ 6,186,000	6,186,000
Contractual rate	5.54%
Junior Subordinated Debt | Town Bankshares Capital Trust I
Subordinated Borrowing [Line Items]
Common Securities	$ 186,000
Trust Preferred Securities	6,000,000
Junior subordinated debentures	$ 6,186,000	6,186,000
Contractual rate	5.54%
Junior Subordinated Debt | First Northwest Capital Trust I
Subordinated Borrowing [Line Items]
Common Securities	$ 155,000
Trust Preferred Securities	5,000,000
Junior subordinated debentures	$ 5,155,000	5,155,000
Contractual rate	5.80%
Junior Subordinated Debt | Suburban Illinois Capital Trust II
Subordinated Borrowing [Line Items]
Common Securities	$ 464,000
Trust Preferred Securities	15,000,000
Junior subordinated debentures	$ 15,464,000	15,464,000
Contractual rate	4.54%
Junior Subordinated Debt | Community Financial Shares Statutory Trust II
Subordinated Borrowing [Line Items]
Common Securities	$ 109,000
Trust Preferred Securities	3,500,000
Junior subordinated debentures	$ 3,609,000	$ 3,609,000
Contractual rate	4.41%
Junior Subordinated Debt | London Interbank Offered Rate (LIBOR) | Wintrust Capital Trust III
Subordinated Borrowing [Line Items]
Debt instrument, basis spread on variable rate	3.25%
Junior Subordinated Debt | London Interbank Offered Rate (LIBOR) | Wintrust Statutory Trust IV
Subordinated Borrowing [Line Items]
Debt instrument, basis spread on variable rate	2.80%
Junior Subordinated Debt | London Interbank Offered Rate (LIBOR) | Wintrust Statutory Trust V
Subordinated Borrowing [Line Items]
Debt instrument, basis spread on variable rate	2.60%
Junior Subordinated Debt | London Interbank Offered Rate (LIBOR) | Wintrust Capital Trust VII
Subordinated Borrowing [Line Items]
Debt instrument, basis spread on variable rate	1.95%
Junior Subordinated Debt | London Interbank Offered Rate (LIBOR) | Wintrust Capital Trust VIII
Subordinated Borrowing [Line Items]
Debt instrument, basis spread on variable rate	1.45%
Junior Subordinated Debt | London Interbank Offered Rate (LIBOR) | Wintrust Capital Trust IX
Subordinated Borrowing [Line Items]
Debt instrument, basis spread on variable rate	1.63%
Junior Subordinated Debt | London Interbank Offered Rate (LIBOR) | Northview Capital Trust I
Subordinated Borrowing [Line Items]
Debt instrument, basis spread on variable rate	3.00%
Junior Subordinated Debt | London Interbank Offered Rate (LIBOR) | Town Bankshares Capital Trust I
Subordinated Borrowing [Line Items]
Debt instrument, basis spread on variable rate	3.00%
Junior Subordinated Debt | London Interbank Offered Rate (LIBOR) | First Northwest Capital Trust I
Subordinated Borrowing [Line Items]
Debt instrument, basis spread on variable rate	3.00%
Junior Subordinated Debt | London Interbank Offered Rate (LIBOR) | Suburban Illinois Capital Trust II
Subordinated Borrowing [Line Items]
Debt instrument, basis spread on variable rate	1.75%
Junior Subordinated Debt | London Interbank Offered Rate (LIBOR) | Community Financial Shares Statutory Trust II
Subordinated Borrowing [Line Items]
Debt instrument, basis spread on variable rate	1.62%