Junior Subordinated Debentures (Summary of Junior Subordinated Debentures) (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Jan. 31, 2016	Aug. 31, 2005
Subordinated Borrowing [Line Items]
Junior subordinated debentures	$ 253,566,000	$ 253,566,000	$ 253,566,000
Wintrust Capital Trust III
Subordinated Borrowing [Line Items]
Common Securities	774,000
Trust Preferred Securities	25,000,000
Junior subordinated debentures	$ 25,774,000
Rate Structure	L+3.25
Contractual rate	4.41%
Issue Date	Apr. 30, 2003
Maturity Date	Apr. 30, 2033
Earliest Redemption Date	Apr. 30, 2008
Wintrust Statutory Trust IV
Subordinated Borrowing [Line Items]
Common Securities	$ 619,000
Trust Preferred Securities	20,000,000
Junior subordinated debentures	$ 20,619,000
Rate Structure	L+2.80
Contractual rate	4.10%
Issue Date	Dec. 31, 2003
Maturity Date	Dec. 31, 2033
Earliest Redemption Date	Dec. 31, 2008
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
Rate Structure	L+2.60
Contractual rate	3.90%
Issue Date	May 31, 2004
Maturity Date	May 31, 2034
Earliest Redemption Date	Jun. 30, 2009
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
Rate Structure	L+1.95
Contractual rate	3.20%
Issue Date	Dec. 31, 2004
Maturity Date	Mar. 31, 2035
Earliest Redemption Date	Mar. 31, 2010
Wintrust Capital Trust VIII
Subordinated Borrowing [Line Items]
Common Securities	$ 1,238,000
Trust Preferred Securities	25,000,000			$ 15,000,000.0	$ 40,000,000.0
Junior subordinated debentures	$ 26,238,000			$ 15,000,000
Rate Structure	L+1.45
Contractual rate	2.75%
Issue Date	Aug. 31, 2005
Maturity Date	Sep. 30, 2035
Earliest Redemption Date	Sep. 30, 2010
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
Rate Structure	L+1.63
Contractual rate	2.88%
Issue Date	Sep. 30, 2006
Maturity Date	Sep. 30, 2036
Earliest Redemption Date	Sep. 30, 2011
Northview Capital Trust I
Subordinated Borrowing [Line Items]
Common Securities	$ 186,000
Trust Preferred Securities	6,000,000
Junior subordinated debentures	$ 6,186,000
Rate Structure	L+3.00
Contractual rate	4.17%
Issue Date	Aug. 31, 2003
Maturity Date	Nov. 30, 2033
Earliest Redemption Date	Aug. 31, 2008
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
Rate Structure	L+3.00
Contractual rate	4.17%
Issue Date	Aug. 31, 2003
Maturity Date	Nov. 30, 2033
Earliest Redemption Date	Aug. 31, 2008
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
Rate Structure	L+3.00
Contractual rate	4.30%
Issue Date	May 31, 2004
Maturity Date	May 31, 2034
Earliest Redemption Date	May 31, 2009
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
Rate Structure	L+1.75
Contractual rate	3.00%
Issue Date	Dec. 31, 2006
Maturity Date	Dec. 31, 2036
Earliest Redemption Date	Dec. 31, 2011
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
Rate Structure	L+1.62
Contractual rate	2.87%
Issue Date	Jun. 30, 2007
Maturity Date	Sep. 30, 2037
Earliest Redemption Date	Jun. 30, 2012
Junior Subordinated Debt
Subordinated Borrowing [Line Items]
Debt, weighted average interest rate	3.45%
London Interbank Offered Rate (LIBOR) | Wintrust Capital Trust III
Subordinated Borrowing [Line Items]
Rate Structure, Incremental interest rate over base rate	3.25%
London Interbank Offered Rate (LIBOR) | Wintrust Statutory Trust IV
Subordinated Borrowing [Line Items]
Rate Structure, Incremental interest rate over base rate	2.80%
London Interbank Offered Rate (LIBOR) | Wintrust Statutory Trust V
Subordinated Borrowing [Line Items]
Rate Structure, Incremental interest rate over base rate	2.60%
London Interbank Offered Rate (LIBOR) | Wintrust Capital Trust VII
Subordinated Borrowing [Line Items]
Rate Structure, Incremental interest rate over base rate	1.95%
London Interbank Offered Rate (LIBOR) | Wintrust Capital Trust VIII
Subordinated Borrowing [Line Items]
Rate Structure, Incremental interest rate over base rate	1.45%
London Interbank Offered Rate (LIBOR) | Wintrust Capital Trust IX
Subordinated Borrowing [Line Items]
Rate Structure, Incremental interest rate over base rate	1.63%
London Interbank Offered Rate (LIBOR) | Northview Capital Trust I
Subordinated Borrowing [Line Items]
Rate Structure, Incremental interest rate over base rate	3.00%
London Interbank Offered Rate (LIBOR) | Town Bankshares Capital Trust I
Subordinated Borrowing [Line Items]
Rate Structure, Incremental interest rate over base rate	3.00%
London Interbank Offered Rate (LIBOR) | First Northwest Capital Trust I
Subordinated Borrowing [Line Items]
Rate Structure, Incremental interest rate over base rate	3.00%
London Interbank Offered Rate (LIBOR) | Suburban Illinois Capital Trust II
Subordinated Borrowing [Line Items]
Rate Structure, Incremental interest rate over base rate	1.75%
London Interbank Offered Rate (LIBOR) | Community Financial Shares Statutory Trust II
Subordinated Borrowing [Line Items]
Rate Structure, Incremental interest rate over base rate	1.62%