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, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Commitments And Contingencies [Line Items]
Letters of credit outstanding				$ 291,800	$ 233,300
Mortgage loans sold				4,484,838	4,076,887	$ 3,869,137
Liability for estimated losses on repurchase and indemnification claims				2,400	2,400
Losses charged against liability				639	183
Unfunded commitments to investment partnerships				29,300
Commitments to invest in partnership for tax credits				323
Customer balances maintained by clearing broker and subject to indemnification				15,800
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 contracts
Commitments And Contingencies [Line Items]
Derivative instrument, contractual amounts				837,200	481,600
Commercial, commercial real estate, and construction loans
Commitments And Contingencies [Line Items]
Commitments to extend loans				5,100,000	4,700,000
Unused home equity lines
Commitments And Contingencies [Line Items]
Commitments to extend loans				800,600	807,900
Residential real estate
Commitments And Contingencies [Line Items]
Commitments to extend loans				$ 595,100	$ 389,700