Schedule of Disposal Groups Including Discontinued Operations Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013
Investor Force
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Revenue (through date of respective sale)		$ 0.8
Actua Corporation’s share of net income (loss) (through date of respective sale)		(0.5)
Channel Intelligence
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Revenue (through date of respective sale)		3.1
Actua Corporation’s share of net income (loss) (through date of respective sale)		(2.5)
Procurian
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Revenue (through date of respective sale)	33.9	103.5
Actua Corporation’s share of net income (loss) (through date of respective sale)	$ 1.7	$ 4.1