Consolidated Businesses - Additional Information (Detail) - USD ($)						3 Months Ended	9 Months Ended
	Oct. 31, 2016	Sep. 16, 2016	Jan. 22, 2016	Nov. 25, 2015	Nov. 03, 2014	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
Business Acquisition [Line Items]
Impact of subsidiary equity transactions							$ 4,453,000	$ 268,000
Payments to acquired additional interest in subsidiaries							5,400,000	4,000,000
Actua's share of consolidated business equity transactions							(1,100,000)
Additional Paid-In Capital
Business Acquisition [Line Items]
Impact of subsidiary equity transactions							4,314,000	$ 1,430,000
FolioDynamix
Business Acquisition [Line Items]
Cash paid for acquisition					$ 201,700,000
Rolled stock options acquired					$ 4,100,000
FolioDynamix | Adjustment
Business Acquisition [Line Items]
Post-closing working capital adjustment						$ 700,000
WellNet | VelocityEHS
Business Acquisition [Line Items]
Cash paid for acquisition				$ 700,000			$ 2,200,000
Intangible assets recorded in acquisition				$ 2,900,000
ErgoAdvocate | VelocityEHS
Business Acquisition [Line Items]
Cash paid for acquisition			$ 1,000,000
Business acquisition, consideration transferred			1,250,000
Liabilities incurred to be paid in one year			$ 250,000
E3 Solutions | VelocityEHS
Business Acquisition [Line Items]
Cash paid for acquisition		$ 2,700,000
Business acquisition, consideration transferred		3,000,000
Liabilities incurred to be paid in equal halves on one year and 18 month anniversaries of the closing		$ 300,000
SAS | FolioDynamix | Subsequent Event
Business Acquisition [Line Items]
Business acquisition, consideration transferred	$ 2,900,000
Business Combination, Consideration Transferred, Liabilities Incurred, Payable Over 15 Month Period	1,000,000
Maximum consideration payable	$ 25,000,000.0