Junior Subordinated Debentures (Summary Of The Company's Junior Subordinated Debentures) (Detail) (USD $)				9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Sep. 30, 2012 Wintrust Capital Trust III	Sep. 30, 2012 Wintrust Statutory Trust IV	Sep. 30, 2012 Wintrust Statutory Trust V	Sep. 30, 2012 Wintrust Capital Trust VII [Member]	Sep. 30, 2012 Wintrust Capital Trust VIII [Member]	Sep. 30, 2012 Wintrust Capital Trust IX [Member]	Sep. 30, 2012 Northview Capital Trust I [Member]	Sep. 30, 2012 Town Bankshares Capital Trust I [Member]	Sep. 30, 2012 First Northwest Capital Trust I [Member]
Common Securities				$ 774,000	$ 619,000	$ 1,238,000	$ 1,550,000	$ 1,238,000	$ 1,547,000	$ 186,000	$ 186,000	$ 155,000
Trust Preferred Securities				25,000,000	20,000,000	40,000,000	50,000,000	40,000,000	50,000,000	6,000,000	6,000,000	5,000,000
Junior subordinated debentures	$ 249,493,000	$ 249,493,000	$ 249,493,000	$ 25,774,000	$ 20,619,000	$ 41,238,000	$ 51,550,000	$ 41,238,000	$ 51,547,000	$ 6,186,000	$ 6,186,000	$ 5,155,000
Rate Structure				L+3.25	L+2.80	L+2.60	L+1.95	L+1.45	L+1.63	L+3.00	L+3.00	L+3.00
Contractual rate				3.71%	3.16%	2.96%	2.34%	1.81%	2.02%	3.44%	3.44%	3.36%
Debt, Weighted Average Interest Rate	4.91%
Issue Date				2003-04	2003-12	2004-05	2004-12	2005-08	2006-09	2003-08	2003-08	2004-05
Maturity Date				04/2033	12/2033	05/2034	03/2035	09/2035	09/2036	11/2033	11/2033	05/2034
Earliest Redemption Date				04/2008	12/2008	06/2009	03/2010	09/2010	09/2011	08/2008	08/2008	05/2009