Commitments And Contingencies (Details) $ in Thousands				12 Months Ended
	Oct. 17, 2018 USD ($) investor plaintiff	Apr. 09, 2018 USD ($)	Feb. 03, 2016 defendant	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Commitments And Contingencies [Line Items]
Letters of credit outstanding, amount				$ 233,300	$ 195,900
Mortgage loans sold				4,076,887	3,869,137	$ 4,468,984
Additional amount related to loss indemnification claims for residential mortgage loans previously sold to investors				2,400	3,000
Losses charged against indemnification liability				183	1,400
Commitments to invest in partnership				13,600
Commitments to invest in partnership for tax credits				914
Customer balances maintained by clearing broker and subject to indemnification				11,300
Lehman Holdings matter
Commitments And Contingencies [Line Items]
Number of defendants other than Wintrust | defendant			150
JPMC matter
Commitments And Contingencies [Line Items]
Amount of damages sought		$ 4,600
Ponzi scheme matter
Commitments And Contingencies [Line Items]
Amount of damages sought	$ 6,000
Number of plaintiffs | plaintiff	2
Number of investors in plaintiff group | investor	42
Forward commitments to sell mortgage loans
Commitments And Contingencies [Line Items]
Notional amount				481,600	551,900
Commercial, commercial real estate, and construction loans
Commitments And Contingencies [Line Items]
Loans and leases receivable, commitments				4,700,000	4,400,000
Home equity
Commitments And Contingencies [Line Items]
Loans and leases receivable, commitments				807,900	826,500
Residential real estate
Commitments And Contingencies [Line Items]
Loans and leases receivable, commitments				$ 389,700	$ 446,300