Acquisitions, Asset Sales, and Divestitures Asset Sales and Divestitures (Details) - Westfield Capital Management Company LLC [Member]	12 Months Ended
	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Nature of Activities Having Continuing Cash Flows after Disposal	12.5% share in Westfield’s revenues (up to an annual maximum of $11.6 million)
Discontinued Operation, Period of Continuing Cash Flows after Disposal	2 years