Commitments, Contingencies and Guarantees	3 Months Ended
Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments, Contingencies and Guarantees	Commitments, Contingencies, and Guarantees Deferred Acquisition Consideration. In addition to the consideration paid by the Company in respect of certain of its acquisitions at closing, additional consideration may be payable, or may be potentially payable based on the achievement of certain threshold levels of earnings. See Notes 2, 5, and 10 for further information. Options to Purchase. Noncontrolling shareholders in certain subsidiaries have the right in certain circumstances to require the Company to acquire the remaining ownership interests held by them. The noncontrolling shareholders’ ability to exercise any such option right is subject to the satisfaction of certain conditions, including conditions requiring notice in advance of exercise and specific employment termination conditions. In addition, these rights cannot be exercised prior to specified staggered exercise dates. The exercise of these rights at their earliest contractual date would result in obligations of the Company to fund the related amounts during 2018 to 2023. It is not determinable, at this time, if or when the owners of these rights will exercise all or a portion of these rights. The amount payable by the Company in the event such rights are exercised is dependent on various valuation formulas and on future events, such as the average earnings of the relevant subsidiary through the date of exercise, the growth rate of the earnings of the relevant subsidiary during that period and, in some cases, the currency exchange rate at the date of payment. Management estimates, assuming that the subsidiaries owned by the Company at March 31, 2018, perform over the relevant future periods at their trailing twelve-month earnings levels, that these rights, if all exercised, could require the Company, to pay an aggregate amount of approximately $15,168 to the owners of such rights in future periods to acquire such ownership interests in the relevant subsidiaries. Of this amount, the Company is entitled, at its option, to fund approximately $199 by the issuance of share capital. In addition, the Company is obligated under similar put option rights to pay an aggregate amount of approximately $33,470 only upon termination of such owner’s employment with the applicable subsidiary or death. The amount the Company would be required to pay to the noncontrolling interest holders should the Company acquire the remaining ownership interests is $5,705 less than the initial redemption value recorded in redeemable noncontrolling interests. Included in redeemable noncontrolling interests at March 31, 2018 was $54,345 of these put options because they are not within the control of the Company. The ultimate amount payable relating to these transactions will vary because it is dependent on the future results of operations of the subject businesses and the timing of when these rights are exercised. Natural Disasters. Certain of the Company’s operations are located in regions of the United States which typically are subject to hurricanes. During the three months ended March 31, 2018 and 2017, these operations did not incur any material costs related to damages resulting from hurricanes. Guarantees. Generally, the Company has indemnified the purchasers of certain assets in the event that a third party asserts a claim against the purchaser that relates to a liability retained by the Company. These types of indemnification guarantees typically extend for a number of years. Historically, the Company has not made any significant indemnification payments under such agreements and no amount has been accrued in the accompanying consolidated financial statements with respect to these indemnification guarantees. The Company continues to monitor the conditions that are subject to guarantees and indemnifications to identify whether it is probable that a loss has occurred, and would recognize any such losses under any guarantees or indemnifications in the period when those losses are probable and estimable. Legal Proceedings. The Company’s operating entities are involved in legal proceedings of various types. While any litigation contains an element of uncertainty, the Company has no reason to believe that the outcome of such proceedings or claims will have a material adverse effect on the financial condition or results of operations of the Company. In addition, the Company is involved in class action suits as described below. Class Action Litigation in Canada. On August 7, 2015, Roberto Paniccia issued a Statement of Claim in the Ontario Superior Court of Justice in the City of Brantford, Ontario seeking to certify a class action suit naming the following as defendants: MDC, former CEO Miles S. Nadal, former CAO Michael C. Sabatino, CFO David Doft and BDO U.S.A. LLP. The Plaintiff alleges violations of section 138.1 of the Ontario Securities Act (and equivalent legislation in other Canadian provinces and territories) as well as common law misrepresentation based on allegedly materially false and misleading statements in the Company’s public statements, as well as omitting to disclose material facts with respect to the SEC investigation. The Company intends to continue to vigorously defend this suit. The plaintiff has served his material for leave to proceed under the Ontario Securities Act and that motion is currently scheduled to be heard on May 15, 2018. A motion by the Company and other defendants to address the scope of the proposed class definition was dismissed and the Company is appealing that decision. Antitrust Subpoena. In 2016, one of the Company’s subsidiary agencies received a subpoena from the U.S. Department of Justice Antitrust Division concerning the Division’s ongoing investigation of production practices in the advertising industry. The Company and its subsidiary are fully cooperating with this confidential investigation. Commitments. At March 31, 2018, the Company had $5,248 of undrawn letters of credit. In addition, the Company has commitments to fund investments in an aggregate amount of $80.

Commitments, Contingencies, and Guarantees

Deferred Acquisition Consideration. In addition to the consideration paid by the Company in respect of certain of its acquisitions at closing, additional consideration may be payable, or may be potentially payable based on the achievement of certain threshold levels of earnings. See Notes 2, 5, and 10 for further information.

Options to Purchase. Noncontrolling shareholders in certain subsidiaries have the right in certain circumstances to require the Company to acquire the remaining ownership interests held by them. The noncontrolling shareholders’ ability to exercise any such option right is subject to the satisfaction of certain conditions, including conditions requiring notice in advance of exercise and specific employment termination conditions. In addition, these rights cannot be exercised prior to specified staggered exercise dates. The exercise of these rights at their earliest contractual date would result in obligations of the Company to fund the related amounts during 2018 to 2023. It is not determinable, at this time, if or when the owners of these rights will exercise all or a portion of these rights.

The amount payable by the Company in the event such rights are exercised is dependent on various valuation formulas and on future events, such as the average earnings of the relevant subsidiary through the date of exercise, the growth rate of the earnings of the relevant subsidiary during that period and, in some cases, the currency exchange rate at the date of payment.

Management estimates, assuming that the subsidiaries owned by the Company at March 31, 2018, perform over the relevant future periods at their trailing twelve-month earnings levels, that these rights, if all exercised, could require the Company, to pay an aggregate amount of approximately $15,168 to the owners of such rights in future periods to acquire such ownership interests in the relevant subsidiaries. Of this amount, the Company is entitled, at its option, to fund approximately $199 by the issuance of share capital.

In addition, the Company is obligated under similar put option rights to pay an aggregate amount of approximately $33,470 only upon termination of such owner’s employment with the applicable subsidiary or death.

The amount the Company would be required to pay to the noncontrolling interest holders should the Company acquire the remaining ownership interests is $5,705 less than the initial redemption value recorded in redeemable noncontrolling interests.

Included in redeemable noncontrolling interests at March 31, 2018 was $54,345 of these put options because they are not within the control of the Company. The ultimate amount payable relating to these transactions will vary because it is dependent on the future results of operations of the subject businesses and the timing of when these rights are exercised.

Natural Disasters. Certain of the Company’s operations are located in regions of the United States which typically are subject to hurricanes. During the three months ended March 31, 2018 and 2017, these operations did not incur any material costs related to damages resulting from hurricanes.

Guarantees. Generally, the Company has indemnified the purchasers of certain assets in the event that a third party asserts a claim against the purchaser that relates to a liability retained by the Company. These types of indemnification guarantees typically extend for a number of years. Historically, the Company has not made any significant indemnification payments under such agreements and no amount has been accrued in the accompanying consolidated financial statements with respect to these indemnification guarantees. The Company continues to monitor the conditions that are subject to guarantees and indemnifications to identify whether it is probable that a loss has occurred, and would recognize any such losses under any guarantees or indemnifications in the period when those losses are probable and estimable.

Legal Proceedings. The Company’s operating entities are involved in legal proceedings of various types. While any litigation contains an element of uncertainty, the Company has no reason to believe that the outcome of such proceedings or claims will have a material adverse effect on the financial condition or results of operations of the Company. In addition, the Company is involved in class action suits as described below.

Class Action Litigation in Canada. On August 7, 2015, Roberto Paniccia issued a Statement of Claim in the Ontario Superior Court of Justice in the City of Brantford, Ontario seeking to certify a class action suit naming the following as defendants: MDC, former CEO Miles S. Nadal, former CAO Michael C. Sabatino, CFO David Doft and BDO U.S.A. LLP. The Plaintiff alleges violations of section 138.1 of the Ontario Securities Act (and equivalent legislation in other Canadian provinces and territories) as well as common law misrepresentation based on allegedly materially false and misleading statements in the Company’s public statements, as well as omitting to disclose material facts with respect to the SEC investigation. The Company intends to continue to vigorously defend this suit. The plaintiff has served his material for leave to proceed under the Ontario Securities Act and that motion is currently scheduled to be heard on May 15, 2018. A motion by the Company and other defendants to address the scope of the proposed class definition was dismissed and the Company is appealing that decision.

Antitrust Subpoena. In 2016, one of the Company’s subsidiary agencies received a subpoena from the U.S. Department of Justice Antitrust Division concerning the Division’s ongoing investigation of production practices in the advertising industry. The Company and its subsidiary are fully cooperating with this confidential investigation.

Commitments. At March 31, 2018, the Company had $5,248 of undrawn letters of credit. In addition, the Company has commitments to fund investments in an aggregate amount of $80.