Junior Subordinated Debentures (Summary Of The Company's Junior Subordinated Debentures) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended				9 Months Ended
	Dec. 31, 2010	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Sep. 30, 2013 Wintrust Capital Trust III	Sep. 30, 2013 Wintrust Statutory Trust IV	Sep. 30, 2013 Wintrust Statutory Trust V	Sep. 30, 2013 Wintrust Capital Trust VII	Sep. 30, 2013 Wintrust Capital Trust VIII	Sep. 30, 2013 Wintrust Capital Trust IX	Sep. 30, 2013 Northview Capital Trust I	Sep. 30, 2013 Town Bankshares Capital Trust I	Sep. 30, 2013 First Northwest Capital Trust I
Subordinated Borrowing [Line Items]
Common Securities					$ 774	$ 619	$ 1,238	$ 1,550	$ 1,238	$ 1,547	$ 186	$ 186	$ 155
Trust Preferred Securities					25,000	20,000	40,000	50,000	40,000	50,000	6,000	6,000	5,000
Junior subordinated debentures		$ 249,493	$ 249,493	$ 249,493	$ 25,774	$ 20,619	$ 41,238	$ 51,550	$ 41,238	$ 51,547	$ 6,186	$ 6,186	$ 5,155
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
Incremental interest rate over base rate					3.25%	2.80%	2.60%	1.95%	1.45%	1.63%	3.00%	3.00%	3.00%
Contractual rate					3.52%	3.05%	2.85%	2.20%	1.70%	1.88%	3.27%	3.27%	3.25%
Debt, Weighted Average Interest Rate		2.44%
Issue Date					Apr. 30, 2003	Dec. 31, 2003	May 31, 2004	Dec. 31, 2004	Aug. 31, 2005	Sep. 30, 2006	Aug. 31, 2003	Aug. 31, 2003	May 31, 2004
Maturity Date	Dec. 15, 2013				Apr. 30, 2033	Dec. 31, 2033	May 31, 2034	Mar. 31, 2035	Sep. 30, 2035	Sep. 30, 2036	Nov. 30, 2033	Nov. 30, 2033	May 31, 2034
Earliest Redemption Date					Apr. 30, 2008	Dec. 31, 2008	Jun. 30, 2009	Mar. 31, 2010	Sep. 30, 2010	Sep. 30, 2011	Aug. 31, 2008	Aug. 31, 2008	May 31, 2009