Acquisitions and Divestitures - Disposals (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Jun. 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	19,625
Fees receivable, net	48,305
Goodwill	246,210
Intangible assets, net	264,120
Other assets (including prepaid expenses and fixed assets)	27,820
Total assets	606,080
Accounts payable and accrued liabilities	26,022
Deferred revenues	68,910
Other liabilities	51,131
Foreign currency translation adjustment	60,310
Total liabilities and foreign currency translation adjustment	$ 206,373