Significant Accounting Policies - Additional Information (Detail)		3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 18, 2016 USD ($)	Sep. 30, 2016 USD ($) customer	Sep. 30, 2015 USD ($) customer	Sep. 30, 2016 USD ($) revenue_source customer	Sep. 30, 2015 USD ($) customer	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Significant Accounting Policies [Line Items]
Restricted cash and cash equivalents		$ 300,000		$ 300,000		$ 400,000
Interest paid		0	$ 0	0	$ 0
Income taxes paid		0	0	0	0
Capital expenditures incurred but not yet paid		200,000	$ 0	900,000	$ 0
Redeemable noncontrolling interests (Note 4, Consolidated Businesses)		9,362,000		9,362,000		10,506,000
Additional paid-in capital		3,572,313,000		3,572,313,000		3,563,848,000
Noncontrolling interests		$ 12,415,000		$ 12,415,000		14,866,000
Actua's Customer Concentration Risk | Consolidated Revenue
Significant Accounting Policies [Line Items]
Number of customers represented for more than 10% of consolidated revenue | customer		0	0	0	0
GovDelivery | Disposed of by sale
Significant Accounting Policies [Line Items]
Proceeds from escrow releases		$ 4,000,000		$ 4,000,000
GovDelivery | Disposed of by sale | Subsequent Event
Significant Accounting Policies [Line Items]
Additional amount of proceeds to be held in escrow subject to indemnification claims	$ 10,000,000
Restatement Adjustment | Correction of Error, Recognition of Permanent Equity
Significant Accounting Policies [Line Items]
Redeemable noncontrolling interests (Note 4, Consolidated Businesses)							$ 4,100,000
Additional paid-in capital							(1,400,000)
Noncontrolling interests							$ (2,700,000)
Bolt
Significant Accounting Policies [Line Items]
Subscription period				1 month
FolioDynamix
Significant Accounting Policies [Line Items]
Impairment loss						$ 39,700,000
Initial subscription arrangement, minimum				3 years
Initial subscription arrangement, maximum				5 years
VelocityEHS
Significant Accounting Policies [Line Items]
Number of sources of revenues (revenue sources) | revenue_source				2