Junior Subordinated Debentures (Narrative) (Detail)		9 Months Ended
	Jan. 22, 2016 USD ($)	Sep. 30, 2017 USD ($) trust Rate	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Jan. 31, 2016 USD ($)	Aug. 31, 2005 USD ($)
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	$ 253,566,000	$ 253,566,000
Gains on early extinguishment of debt		0	$ 4,305,000
Junior Subordinated Debt
Subordinated Borrowing [Line Items]
Junior subordinated debentures		$ 253,566,000
Debt, weighted average interest rate | Rate		3.52%
Period of deferred payment, not to exceed		60 months
Tier one risk based capital		$ 0
Tier two risk based capital		245,500,000
Junior Subordinated Debt | Wintrust Capital Trust VIII
Subordinated Borrowing [Line Items]
Trust preferred securities		25,000,000			$ 15,000,000.0	$ 40,000,000.0
Junior subordinated debentures		$ 26,238,000			$ 15,000,000
Gains on early extinguishment of debt	$ 4,300,000