Investments - Investment Income (Details) (USD $)	12 Months Ended					3 Months Ended	12 Months Ended		36 Months Ended		3 Months Ended
	Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Private Investments Investment	Dec. 31, 2013 Investment, One	Dec. 31, 2012 Investment, One	Dec. 31, 2011 Investment, One	Dec. 31, 2013 Investment, One	Sep. 30, 2013 Investment, One	Dec. 31, 2013 Investment, Two
Investment [Line Items]
Gross realized gains	$ 7,050,000		$ 15,018,000	$ 4,846,000
Gross realized losses	(1,480,000)	[1]	(2,637,000)	(1,795,000)
Investment income	5,570,000		12,381,000	3,051,000
Number of Investments					2
Investments accounted for under cost method	135,819,000		112,333,000			0			0	350,000
Impairment loss						$ 350,000	$ 400,000	$ 200,000	$ 853,000		$ 488,000

[1] Includes an impairment loss aggregating $853 thousand primarily related to investment in two private life science companies. During the three months ended December 31, 2013, we reduced the cost basis of an investment in a life science company from $350 thousand to zero. The cost basis of this investment was reduced by $400 thousand and $200 thousand in aggregate during the years ended December 31, 2012 and 2011, respectively, to our estimate of fair value as of the date of each reduction. During the three months ended December 31, 2013, we also reduced the cost basis of another investment in a life science company by $488 thousand to its estimated fair value. This life science company was subsequently acquired by a public company in the first quarter of 2014 at a value approximating our cost basis.