Supplemental Balance Sheet, Income Statement and Cash Flow Information (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Supplemental Balance Sheet, Income Statement and Cash Flow Information
Gain (loss) on sale of debt securities and gains (losses) from long term investments		$ 18,000,000	$ 4,200,000
Net unrealized gains (losses) from trading securities	41,100,000	800,000	4,400,000
Realized gain on short-term and long term investments	14,500,000
Additional disclosure
Pre-tax (losses) gains on purchases of senior exchangeable notes		(58,000)	(7,042,000)
0.94% Senior Exchangeable Notes Due May 2011
Additional disclosure
Pre-tax (losses) gains on purchases of senior exchangeable notes		1,000,000	(7,000,000)
Interest rate on senior note due (as a percent)	0.94%
NFR Energy
Additional disclosure
Gain on sale of equity interest	160,000,000
Peak
Additional disclosure
Gain on acquisition of equity method investment		$ 13,100,000