Junior Subordinated Debentures Junior Subordinated Debentures (Summary of Junior Subordinated Debentures) (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Subordinated Borrowing [Line Items]
Junior subordinated debentures	$ 268,566	$ 249,493	$ 249,493
Wintrust Capital Trust III
Subordinated Borrowing [Line Items]
Common Securities	774
Trust Preferred Securities	25,000
Junior subordinated debentures	$ 25,774
Rate Structure	L+3.25
Contractual rate	3.54%
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
Trust Preferred Securities	20,000
Junior subordinated debentures	$ 20,619
Rate Structure	L+2.80
Contractual rate	3.13%
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
Trust Preferred Securities	40,000
Junior subordinated debentures	$ 41,238
Rate Structure	L+2.60
Contractual rate	2.93%
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
Trust Preferred Securities	50,000
Junior subordinated debentures	$ 51,550
Rate Structure	L+1.95
Contractual rate	2.29%
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
Trust Preferred Securities	40,000
Junior subordinated debentures	$ 41,238
Rate Structure	L+1.45
Contractual rate	1.78%
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
Trust Preferred Securities	50,000
Junior subordinated debentures	$ 51,547
Rate Structure	L+1.63
Contractual rate	1.97%
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
Trust Preferred Securities	6,000
Junior subordinated debentures	$ 6,186
Rate Structure	L+3.00
Contractual rate	3.30%
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
Trust Preferred Securities	6,000
Junior subordinated debentures	$ 6,186
Rate Structure	L+3.00
Contractual rate	3.30%
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
Trust Preferred Securities	5,000
Junior subordinated debentures	$ 5,155
Rate Structure	L+3.00
Contractual rate	3.33%
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
Trust Preferred Securities	15,000
Junior subordinated debentures	$ 15,464
Rate Structure	L+1.75
Contractual rate	2.09%
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
Trust Preferred Securities	3,500
Junior subordinated debentures	$ 3,609
Rate Structure	L+1.62
Contractual rate	1.96%
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	2.48%
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%