Junior Subordinated Debentures (Summary Of The Company's Junior Subordinated Debentures) (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2010	Dec. 31, 2012	Mar. 31, 2012
Debt Instrument, Maturity Date	Dec. 15, 2013	Dec. 15, 2013
Junior subordinated debentures	$ 249,493,000		$ 249,493,000	$ 249,493,000
Debt, Weighted Average Interest Rate	4.88%
Wintrust Capital Trust III
Incremental interest rate over base rate	3.25%
Debt Instrument, Issuance Date	Apr. 30, 2003
Debt Instrument, Maturity Date	Apr. 30, 2033
Common Securities	774,000
Trust Preferred Securities	25,000,000
Junior subordinated debentures	25,774,000
Rate Structure	L+3.25
Contractual rate	3.54%
Earliest Redemption Date	04/2008
Wintrust Statutory Trust IV
Incremental interest rate over base rate	2.80%
Debt Instrument, Issuance Date	Dec. 31, 2003
Debt Instrument, Maturity Date	Dec. 31, 2033
Common Securities	619,000
Trust Preferred Securities	20,000,000
Junior subordinated debentures	20,619,000
Rate Structure	L+2.80
Contractual rate	3.08%
Earliest Redemption Date	12/2008
Wintrust Statutory Trust V
Incremental interest rate over base rate	2.60%
Debt Instrument, Issuance Date	May 31, 2004
Debt Instrument, Maturity Date	May 31, 2034
Common Securities	1,238,000
Trust Preferred Securities	40,000,000
Junior subordinated debentures	41,238,000
Rate Structure	L+2.60
Contractual rate	2.88%
Earliest Redemption Date	06/2009
Wintrust Capital Trust VII [Member]
Incremental interest rate over base rate	1.95%
Debt Instrument, Issuance Date	Dec. 31, 2004
Debt Instrument, Maturity Date	Mar. 31, 2035
Common Securities	1,550,000
Trust Preferred Securities	50,000,000
Junior subordinated debentures	51,550,000
Rate Structure	L+1.95
Contractual rate	2.23%
Earliest Redemption Date	03/2010
Wintrust Capital Trust VIII [Member]
Incremental interest rate over base rate	1.45%
Debt Instrument, Issuance Date	Aug. 31, 2005
Debt Instrument, Maturity Date	Sep. 30, 2035
Common Securities	1,238,000
Trust Preferred Securities	40,000,000
Junior subordinated debentures	41,238,000
Rate Structure	L+1.45
Contractual rate	1.73%
Earliest Redemption Date	09/2010
Wintrust Capital Trust IX [Member]
Incremental interest rate over base rate	1.63%
Debt Instrument, Issuance Date	Sep. 30, 2006
Debt Instrument, Maturity Date	Sep. 30, 2036
Common Securities	1,547,000
Trust Preferred Securities	50,000,000
Junior subordinated debentures	51,547,000
Rate Structure	L+1.63
Contractual rate	1.91%
Earliest Redemption Date	09/2011
Northview Capital Trust I [Member]
Incremental interest rate over base rate	3.00%
Debt Instrument, Issuance Date	Aug. 31, 2003
Debt Instrument, Maturity Date	Nov. 30, 2033
Common Securities	186,000
Trust Preferred Securities	6,000,000
Junior subordinated debentures	6,186,000
Rate Structure	L+3.00
Contractual rate	3.30%
Earliest Redemption Date	08/2008
Town Bankshares Capital Trust I [Member]
Incremental interest rate over base rate	3.00%
Debt Instrument, Issuance Date	Aug. 31, 2003
Debt Instrument, Maturity Date	Nov. 30, 2033
Common Securities	186,000
Trust Preferred Securities	6,000,000
Junior subordinated debentures	6,186,000
Rate Structure	L+3.00
Contractual rate	3.30%
Earliest Redemption Date	08/2008
First Northwest Capital Trust I [Member]
Incremental interest rate over base rate	3.00%
Debt Instrument, Issuance Date	May 31, 2004
Debt Instrument, Maturity Date	May 31, 2034
Common Securities	155,000
Trust Preferred Securities	5,000,000
Junior subordinated debentures	$ 5,155,000
Rate Structure	L+3.00
Contractual rate	3.28%
Earliest Redemption Date	05/2009
Junior Subordinated Debt [Member]
Debt, Weighted Average Interest Rate	2.47%