Commitments and Contingencies	12 Months Ended
Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies The Company has outstanding, at any time, a number of commitments to extend credit. These commitments include revolving home equity line and other credit agreements, term loan commitments and standby and commercial letters of credit. Standby and commercial letters of credit are conditional commitments issued to guarantee the performance of a customer to a third party. Standby letters of credit are contingent upon the failure of the customer to perform according to the terms of the underlying contract with the third party, while commercial letters of credit are issued specifically to facilitate commerce and typically result in the commitment being drawn on when the underlying transaction is consummated between the customer and the third party. These commitments involve, to varying degrees, elements of credit and interest rate risk in excess of the amounts recognized in the Consolidated Statements of Condition. Since many of the commitments are expected to expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. The Company uses the same credit policies in making commitments as it does for on-balance sheet instruments. Commitments to extend commercial, commercial real estate and construction loans totaled $4.2 billion and $3.7 billion as of December 31, 2016 and 2015, respectively, and unused home equity lines totaled $836.2 million and $855.1 million as of December 31, 2016 and 2015, respectively. Standby and commercial letters of credit totaled $205.9 million at December 31, 2016 and $176.1 million at December 31, 2015. In addition, at December 31, 2016 and 2015, the Company had approximately $529.5 million and $532.5 million, respectively, in commitments to fund residential mortgage loans to be sold into the secondary market. These lending commitments are also considered derivative instruments. The Company also enters into forward contracts for the future delivery of residential mortgage loans at specified interest rates to reduce the interest rate risk associated with commitments to fund loans as well as mortgage loans held-for-sale. These forward contracts are also considered derivative instruments and had contractual amounts of approximately $773.4 million at December 31, 2016 and $753.9 million at December 31, 2015. See Note 20, “Derivative Financial Instruments,” for further discussion on derivative instruments. The Company enters into residential mortgage loan sale agreements with investors in the normal course of business. These agreements usually require certain representations concerning credit information, loan documentation, collateral and insurability. On occasion, investors have requested the Company to indemnify them against losses on certain loans or to repurchase loans which the investors believe do not comply with applicable representations. Management maintains a liability for estimated losses on loans expected to be repurchased or on which indemnification is expected to be provided and regularly evaluates the adequacy of this recourse liability based on trends in repurchase and indemnification requests, actual loss experience, known and inherent risks in the loans, and current economic conditions. The Company sold approximately $4.5 billion of mortgage loans in 2016 and $4.0 billion in 2015. The liability for estimated losses on repurchase and indemnification claims for residential mortgage loans previously sold to investors was $4.2 million and $4.0 million at December 31, 2016 and 2015, respectively, and was included in other liabilities on the Consolidated Statements of Condition. Losses charged against the liability were $552,000 in 2016 as compared to $1.1 million in 2015. These losses relate to mortgages which experienced early payment and other defaults meeting certain representation and warranty recourse requirements. The Company has unfunded commitments to investment partnerships that qualify for CRA purposes totaling $10.9 million as of December 31, 2016. Of these commitments, $4.7 million related to legally-binding unfunded commitments for tax-credit investments and was included within other assets and other liabilities on the consolidated statements of financial condition. The Company utilizes an out-sourced securities clearing platform and has agreed to indemnify the clearing broker of WHI for losses that it may sustain from the customer accounts introduced by WHI. As of December 31, 2016, the total amount of customer balances maintained by the clearing broker and subject to indemnification was approximately $21.3 million. WHI seeks to control the risks associated with its customers’ activities by requiring customers to maintain margin collateral in compliance with various regulatory and internal guidelines. In accordance with applicable accounting principles, the Company establishes an accrued liability for litigation and threatened litigation actions and proceedings when those actions present loss contingencies which are both probable and estimable. In actions for which a loss is reasonably possible in future periods, the Company determines whether it can estimate a loss or range of possible loss. To determine whether a possible loss is estimable, the Company reviews and evaluates its material litigation on an ongoing basis, in conjunction with any outside counsel handling the matter, in light of potentially relevant factual and legal developments. This review may include information learned through the discovery process, rulings on substantive or dispositive motions, and settlement discussions. On January 15, 2015, Lehman Brothers Holdings, Inc. (“Lehman Holdings”) sent a demand letter asserting that Wintrust Mortgage must indemnify it for losses arising from loans sold by Wintrust Mortgage to Lehman Brothers Bank, FSB under a Loan Purchase Agreement between Wintrust Mortgage, as successor to SGB Corporation, and Lehman Brothers Bank. The demand was the precursor for triggering the alternative dispute resolution process mandated by the U.S. Bankruptcy Court for the Southern District of New York. Lehman Holdings triggered the mandatory alternative dispute resolution process on October 16, 2015. On February 3, 2016, following a ruling by the federal Court of Appeals for the Tenth Circuit that was adverse to Lehman Holdings on the statute of limitations that is applicable to similar loan purchase claims, Lehman Holdings filed a complaint against Wintrust Mortgage and 150 other entities from which it had purchased loans in the U.S. Bankruptcy Court for the Southern District of New York. The mandatory mediation was held on March 16, 2016, but did not result in a consensual resolution of the dispute. The court entered a case management order governing the litigation on November 1, 2016. Lehman Holdings filed an amended complaint against Wintrust Mortgage on December 29, 2016. Wintrust Mortgage’s response to the amended complaint is due on March 1, 2017. The Company has reserved an amount for the Lehman Holdings action that is immaterial to its results of operations or financial condition. Such litigation and threatened litigation actions necessarily involve substantial uncertainty and it is not possible at this time to predict the ultimate resolution or to determine whether, or to what extent, any loss with respect to these legal proceedings may exceed the amounts reserved by the Company. On August 28, 2015, Wintrust Mortgage received a demand from RFC Liquidating Trust asserting that Wintrust Mortgage is liable to it for losses arising from loans sold by Wintrust Mortgage or its predecessors to Residential Funding Company LLC and/or related entities. No litigation has been initiated and the range of liability is not reasonably estimable at this time and it is not foreseeable when sufficient information will become available to provide a basis for recording a reserve, should a reserve ultimately be required. On August 13, 2015, BMO Harris Financial Advisors (“BHFA”) filed an arbitration demand with the FINRA seeking damages and a permanent injunction and a complaint with the Circuit Court for Cook County, Illinois seeking a temporary restraining order against one of its former financial advisors and a current financial advisor with WHI. A narrow and limited temporary injunction was entered and the matter was referred to FINRA for arbitration. In November 2015, BHFA added WHI as a co-defendant in the arbitration action, alleging that WHI tortiously interfered with BHFA’s contract with its former financial advisor. A hearing on the merits was held on September 12 - 15, 2016. On October 11, 2016, the FINRA panel issued a damages award against WHI for $1,537,500. The parties agreed to settle the matter for a reduced amount on November 3, 2016. In addition, in the ordinary course of business, there are legal proceedings pending against the Company and its subsidiaries. Management does not believe that a material loss related to these matters is reasonably probable.

Commitments and Contingencies

The Company has outstanding, at any time, a number of commitments to extend credit. These commitments include revolving home equity line and other credit agreements, term loan commitments and standby and commercial letters of credit. Standby and commercial letters of credit are conditional commitments issued to guarantee the performance of a customer to a third party. Standby letters of credit are contingent upon the failure of the customer to perform according to the terms of the underlying contract with the third party, while commercial letters of credit are issued specifically to facilitate commerce and typically result in the commitment being drawn on when the underlying transaction is consummated between the customer and the third party.

These commitments involve, to varying degrees, elements of credit and interest rate risk in excess of the amounts recognized in the Consolidated Statements of Condition. Since many of the commitments are expected to expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. The Company uses the same credit policies in making commitments as it does for on-balance sheet instruments. Commitments to extend commercial, commercial real estate and construction loans totaled $4.2 billion and $3.7 billion as of December 31, 2016 and 2015, respectively, and unused home equity lines totaled $836.2 million and $855.1 million as of December 31, 2016 and 2015, respectively. Standby and commercial letters of credit totaled $205.9 million at December 31, 2016 and $176.1 million at December 31, 2015.

In addition, at December 31, 2016 and 2015, the Company had approximately $529.5 million and $532.5 million, respectively, in commitments to fund residential mortgage loans to be sold into the secondary market. These lending commitments are also considered derivative instruments. The Company also enters into forward contracts for the future delivery of residential mortgage loans at specified interest rates to reduce the interest rate risk associated with commitments to fund loans as well as mortgage loans held-for-sale. These forward contracts are also considered derivative instruments and had contractual amounts of approximately $773.4 million at December 31, 2016 and $753.9 million at December 31, 2015. See Note 20, “Derivative Financial Instruments,” for further discussion on derivative instruments.

The Company enters into residential mortgage loan sale agreements with investors in the normal course of business. These agreements usually require certain representations concerning credit information, loan documentation, collateral and insurability. On occasion, investors have requested the Company to indemnify them against losses on certain loans or to repurchase loans which the investors believe do not comply with applicable representations. Management maintains a liability for estimated losses on loans expected to be repurchased or on which indemnification is expected to be provided and regularly evaluates the adequacy of this recourse liability based on trends in repurchase and indemnification requests, actual loss experience, known and inherent risks in the loans, and current economic conditions.

The Company sold approximately $4.5 billion of mortgage loans in 2016 and $4.0 billion in 2015. The liability for estimated losses on repurchase and indemnification claims for residential mortgage loans previously sold to investors was $4.2 million and $4.0 million at December 31, 2016 and 2015, respectively, and was included in other liabilities on the Consolidated Statements of Condition. Losses charged against the liability were $552,000 in 2016 as compared to $1.1 million in 2015. These losses relate to mortgages which experienced early payment and other defaults meeting certain representation and warranty recourse requirements.

The Company has unfunded commitments to investment partnerships that qualify for CRA purposes totaling $10.9 million as of December 31, 2016. Of these commitments, $4.7 million related to legally-binding unfunded commitments for tax-credit investments and was included within other assets and other liabilities on the consolidated statements of financial condition.

The Company utilizes an out-sourced securities clearing platform and has agreed to indemnify the clearing broker of WHI for losses that it may sustain from the customer accounts introduced by WHI. As of December 31, 2016, the total amount of customer balances maintained by the clearing broker and subject to indemnification was approximately $21.3 million. WHI seeks to control the risks associated with its customers’ activities by requiring customers to maintain margin collateral in compliance with various regulatory and internal guidelines.

In accordance with applicable accounting principles, the Company establishes an accrued liability for litigation and threatened litigation actions and proceedings when those actions present loss contingencies which are both probable and estimable. In actions for which a loss is reasonably possible in future periods, the Company determines whether it can estimate a loss or range of possible loss. To determine whether a possible loss is estimable, the Company reviews and evaluates its material litigation on an ongoing basis, in conjunction with any outside counsel handling the matter, in light of potentially relevant factual and legal developments. This review may include information learned through the discovery process, rulings on substantive or dispositive motions, and settlement discussions.

On January 15, 2015, Lehman Brothers Holdings, Inc. (“Lehman Holdings”) sent a demand letter asserting that Wintrust Mortgage must indemnify it for losses arising from loans sold by Wintrust Mortgage to Lehman Brothers Bank, FSB under a Loan Purchase Agreement between Wintrust Mortgage, as successor to SGB Corporation, and Lehman Brothers Bank. The demand was the precursor for triggering the alternative dispute resolution process mandated by the U.S. Bankruptcy Court for the Southern District of New York. Lehman Holdings triggered the mandatory alternative dispute resolution process on October 16, 2015. On February 3, 2016, following a ruling by the federal Court of Appeals for the Tenth Circuit that was adverse to Lehman Holdings on the statute of limitations that is applicable to similar loan purchase claims, Lehman Holdings filed a complaint against Wintrust Mortgage and 150 other entities from which it had purchased loans in the U.S. Bankruptcy Court for the Southern District of New York. The mandatory mediation was held on March 16, 2016, but did not result in a consensual resolution of the dispute. The court entered a case management order governing the litigation on November 1, 2016. Lehman Holdings filed an amended complaint against Wintrust Mortgage on December 29, 2016. Wintrust Mortgage’s response to the amended complaint is due on March 1, 2017.

The Company has reserved an amount for the Lehman Holdings action that is immaterial to its results of operations or financial condition. Such litigation and threatened litigation actions necessarily involve substantial uncertainty and it is not possible at this time to predict the ultimate resolution or to determine whether, or to what extent, any loss with respect to these legal proceedings may exceed the amounts reserved by the Company.

On August 28, 2015, Wintrust Mortgage received a demand from RFC Liquidating Trust asserting that Wintrust Mortgage is liable to it for losses arising from loans sold by Wintrust Mortgage or its predecessors to Residential Funding Company LLC and/or related entities. No litigation has been initiated and the range of liability is not reasonably estimable at this time and it is not foreseeable when sufficient information will become available to provide a basis for recording a reserve, should a reserve ultimately be required.

On August 13, 2015, BMO Harris Financial Advisors (“BHFA”) filed an arbitration demand with the FINRA seeking damages and a permanent injunction and a complaint with the Circuit Court for Cook County, Illinois seeking a temporary restraining order against one of its former financial advisors and a current financial advisor with WHI. A narrow and limited temporary injunction was entered and the matter was referred to FINRA for arbitration. In November 2015, BHFA added WHI as a co-defendant in the arbitration action, alleging that WHI tortiously interfered with BHFA’s contract with its former financial advisor. A hearing on the merits was held on September 12 - 15, 2016. On October 11, 2016, the FINRA panel issued a damages award against WHI for $1,537,500. The parties agreed to settle the matter for a reduced amount on November 3, 2016.

In addition, in the ordinary course of business, there are legal proceedings pending against the Company and its subsidiaries. Management does not believe that a material loss related to these matters is reasonably probable.