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Fair Value Measurements - Level 3 Redeemable Noncontrolling Interests (Details) - USD ($) $ in Thousands			12 Months Ended
	Nov. 14, 2017	Oct. 17, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 15, 2018
Changes in fair value of the Company’s Level 3 redeemable noncontrolling interests
Issuance of common stock in connection with Openwave acquisition				$ 22,000
Common stock, shares outstanding (in shares)			46,965,000	45,292,000
Redeemable Noncontrolling Interests
Changes in fair value of the Company’s Level 3 redeemable noncontrolling interests
Balance at beginning of period			$ 25,280
Fair value and other adjustments			9,291
Net loss attributable to interests in subsidiaries			(9,291)
Balance at end of period			25,280	$ 25,280
Intralinks Holdings, Inc.
Changes in fair value of the Company’s Level 3 redeemable noncontrolling interests
Issuance of common stock in connection with Openwave acquisition		$ 977,300	$ 4,700	$ 0	$ 0
Convertible Preferred Stock \| Silver Private Holdings I, LLC
Changes in fair value of the Company’s Level 3 redeemable noncontrolling interests
Issuance of common stock in connection with Openwave acquisition		$ 185,000
Silver Private Holdings I, LLC
Changes in fair value of the Company’s Level 3 redeemable noncontrolling interests
Put right consideration	$ 87,300
Silver Private Holdings I, LLC \| Subsequent Event \| Silver Private Holdings I, LLC
Changes in fair value of the Company’s Level 3 redeemable noncontrolling interests
Common stock, shares outstanding (in shares)						5,994,667