Discontinued Operations - Additional Information (Details) - USD ($)				3 Months Ended		9 Months Ended	12 Months Ended
	Sep. 25, 2017	Sep. 23, 2017	Oct. 18, 2016	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2017	Dec. 31, 2016	Jun. 30, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment of cost method investments						$ 0	$ 0
Bolt and VelocityEHS
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash proceeds from divestiture of business		$ 354,000,000
FolioDynamix
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash proceeds from divestiture of business	$ 195,000,000
GovDelivery | Disposed of by sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration			$ 153,000,000
Proceeds from divestiture of business, net of cash divested			133,000,000
Additional amount of proceeds to be held in escrow subject to indemnification claims			$ 10,000,000
Gain (loss) on disposal of discontinued operation					$ 124,800,000
SAS Capital Management, LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Fair value of earn-out liability				$ 1,300,000		$ 1,300,000		$ 8,600,000
Gain recognized on earn-out				$ 7,300,000