Investments (Detail) (USD $)	3 Months Ended					0 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Mar. 31, 2014 Venture Capital Funds investment	Mar. 31, 2014 Promissory Note	Jan. 31, 2013 Again Faster	Mar. 31, 2014 iGo	Dec. 31, 2013 iGo	Aug. 23, 2013 iGo	Mar. 31, 2014 Again Faster	Dec. 31, 2013 Again Faster	Jan. 31, 2013 Again Faster	Mar. 31, 2014 Partnership	Mar. 31, 2014 Partnership Venture Capital Funds
Sales of marketable securities	$ 40,579,000	$ 8,315,000
Membership interest (as a percent)												40.00%
Total cash consideration						4,000,000
Shares acquired (in shares)									1,316,866
Total consideration									5,200,000
Ownership							44.70%	44.70%	44.70%	40.00%	40.00%
Value of investment							4,100,000
Number of investments				2
Cost-method investments	28,826,000		25,844,000										25,000,000
Fair value of cost method investments													28,500,000
Other investments					$ 3,000,000									$ 800,000