Acquisitions and Divestitures - Disposals (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash equivalents	$ 0	$ 10,000	$ 0	$ 0
Disposal Group, Held-for-sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash equivalents	19,624
Fees receivable, net	60,077
Goodwill	315,645
Intangible assets, net	302,415
Other assets (including prepaid expenses and fixed assets)	29,725
Total assets	727,486
Accounts payable and accrued liabilities	29,780
Deferred revenues	85,970
Other liabilities	50,743
Foreign currency translation adjustment	60,160
Total liabilities and foreign currency translation adjustment	$ 226,653