Investments (Detail) (USD $)	3 Months Ended		6 Months Ended					1 Months Ended				1 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Jun. 30, 2014 Venture Capital Funds	Jun. 30, 2014 Promissory Note	Jan. 31, 2013 Again Faster	Jun. 30, 2014 iGo	Dec. 31, 2013 iGo	Aug. 31, 2013 iGo	May 31, 2014 API	Jun. 30, 2013 API	Jun. 30, 2014 API	Jun. 30, 2014 Again Faster	Dec. 31, 2013 Again Faster	Jan. 31, 2013 Again Faster	Jun. 30, 2014 Partnership	Jun. 30, 2014 Securities Loaned or Sold under Agreements to Repurchase
Derivative Liability, Fair Value, Gross Liability	$ 232,198,000		$ 232,198,000		$ 240,394,000														$ 19,300,000
Realized loss on financial instrument obligation	(669,000)	0	(669,000)	0
Sales of marketable securities	55,200,000	36,800,000	95,740,000	45,065,000
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 (as a percent)									44.70%	44.70%	44.70%	20.50%		20.60%	40.00%	40.00%
Number of shares held												11,377,192
Number of shares purchased												1,666,666
Loss on change to equity method at fair value	568,000	0	568,000	0									568,000
Value of investment									4,200,000					31,330,000
Cost-method investments	28,540,000		28,540,000		25,844,000													25,000,000
Fair value of cost method investments																		33,000,000
Other investments						$ 500,000	$ 3,000,000