Junior Subordinated Debentures (Narrative) (Detail)		9 Months Ended
	Jan. 22, 2016 USD ($)	Sep. 30, 2016 USD ($) trust Rate	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Subordinated Borrowing [Line Items]
Percentage ownership interest in subsidiary trusts		100.00%
Number of unconsolidated subsidiary trusts | trust		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		$ 253,566,000	$ 268,566,000	$ 268,566,000
Gains on early extinguishment of debt		4,305,000	$ 0
Wintrust Capital Trust VIII
Subordinated Borrowing [Line Items]
Trust Preferred Securities	$ 15,000,000.0	25,000,000		40,000,000.0
Junior subordinated debentures	15,000,000	$ 26,238,000
Gains on early extinguishment of debt	$ 4,300,000
Junior Subordinated Debt
Subordinated Borrowing [Line Items]
Debt, weighted average interest rate | Rate		3.02%
Debt, Hedge Adjusted Weighted Average Interest Rate | Rate		3.71%
Tier One Risk Based Capital		$ 0		65,100,000
Tier Two Risk Based Capital		$ 245,500,000		$ 195,400,000
Junior Subordinated Debt | Maximum
Subordinated Borrowing [Line Items]
Period of deferred payment, not to exceed		60 months