Junior Subordinated Debentures (Narrative) (Detail) - USD ($) $ in Thousands		3 Months Ended
	Jan. 22, 2016	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Subordinated Borrowing [Line Items]
Percentage ownership interest in subsidiary trusts		100.00%
Number of unconsolidated subsidiary trusts		11
Common securities, approximate percentage of junior subordinated debentures		3.00%
Trust preferred securities, approximate percentage of junior subordinated debentures		97.00%
Junior subordinated debentures		$ 253,566	$ 249,493	$ 268,566
Gains on early extinguishment of debt		$ 4,305	0
Consecutive quarters of deferred payment		20
Wintrust Capital Trust VIII
Subordinated Borrowing [Line Items]
Trust Preferred Securities	$ 15,000	$ 25,000		40,000
Junior subordinated debentures	15,000	$ 26,238
Gains on early extinguishment of debt	$ 4,300
Junior Subordinated Debt
Subordinated Borrowing [Line Items]
Debt, weighted average interest rate		2.83%
Debt, Hedge Adjusted Weighted Average Interest Rate		3.71%
Tier One Risk Based Capital		$ 0	60,500	65,100
Tier Two Risk Based Capital		245,500	$ 181,500	$ 195,400
Cash Flow Hedge of Junior Subordinated Debentures | Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swaps and Caps
Subordinated Borrowing [Line Items]
Notional amount		$ 225,000