Business Combinations	12 Months Ended
Dec. 31, 2017
Business Combinations [Abstract]
Business Combinations	Business Combinations In 2017, we completed four acquisitions, which increased goodwill $65.3 million. Also, we acquired additional equity interests in certain majority owned subsidiaries in 2017, which are accounted for as equity transactions and no additional goodwill was recorded. None of these acquisitions, either individually or in the aggregate, was material to our results of operations or financial position. The evaluation of potential acquisitions is based on various factors, including specialized know-how, reputation, geographic coverage, competitive position and service offerings, as well as our experience and judgment. Our acquisition strategy is focused on acquiring the expertise of an assembled workforce in order to continue to build upon the core capabilities of our strategic business platforms and agency brands, through the expansion of their geographic area or their service capabilities to better serve our clients. Certain acquisitions include an initial payment at closing and provide for future additional contingent purchase price payments (earn-outs), which are derived using the performance of the acquired entity and are based on predetermined formulas. Contingent purchase price obligations at December 31, 2017 and 2016 were $215.6 million and $386.1 million, respectively, of which $92.6 million and $190.8 million, respectively, are included in other current liabilities. For each acquisition, we undertake a detailed review to identify other intangible assets that are required to be valued separately. We use several market participant measurements to determine fair value. This approach includes consideration of similar and recent transactions, as well as utilizing discounted expected cash flow methodologies and when available and as appropriate, we use comparative market multiples to supplement our analysis. As is typical for most service businesses, a substantial portion of the intangible asset value we acquire is the specialized know-how of the workforce, which is treated as part of goodwill and is not valued separately. A significant portion of the identifiable intangible assets acquired is derived from customer relationships, including the related customer contracts, as well as trade names. One of the primary drivers in executing our acquisition strategy is the existence of, or the ability to, expand our existing client relationships. The expected benefits of our acquisitions are typically shared across multiple agencies and regions.

Business Combinations

In 2017, we completed four acquisitions, which increased goodwill $65.3 million. Also, we acquired additional equity interests in certain majority owned subsidiaries in 2017, which are accounted for as equity transactions and no additional goodwill was recorded. None of these acquisitions, either individually or in the aggregate, was material to our results of operations or financial position.

The evaluation of potential acquisitions is based on various factors, including specialized know-how, reputation, geographic coverage, competitive position and service offerings, as well as our experience and judgment. Our acquisition strategy is focused on acquiring the expertise of an assembled workforce in order to continue to build upon the core capabilities of our strategic business platforms and agency brands, through the expansion of their geographic area or their service capabilities to better serve our clients. Certain acquisitions include an initial payment at closing and provide for future additional contingent purchase price payments (earn-outs), which are derived using the performance of the acquired entity and are based on predetermined formulas. Contingent purchase price obligations at December 31, 2017 and 2016 were $215.6 million and $386.1 million, respectively, of which $92.6 million and $190.8 million, respectively, are included in other current liabilities.

For each acquisition, we undertake a detailed review to identify other intangible assets that are required to be valued separately. We use several market participant measurements to determine fair value. This approach includes consideration of similar and recent transactions, as well as utilizing discounted expected cash flow methodologies and when available and as appropriate, we use comparative market multiples to supplement our analysis. As is typical for most service businesses, a substantial portion of the intangible asset value we acquire is the specialized know-how of the workforce, which is treated as part of goodwill and is not valued separately. A significant portion of the identifiable intangible assets acquired is derived from customer relationships, including the related customer contracts, as well as trade names. One of the primary drivers in executing our acquisition strategy is the existence of, or the ability to, expand our existing client relationships. The expected benefits of our acquisitions are typically shared across multiple agencies and regions.