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Cash and Cash Equivalents and Investments (Details 1) (USD $)
In Thousands
6 Months Ended 12 Months Ended
Jun. 30, 2011
Dec. 31, 2010
Cash and cash equivalents and short-term investments    
Cash and cash equivalents, fair value $ 528,822 $ 641,702
Short-term investments:    
Trading equity securities, fair value 12,970 19,630
Trading equity securities, gross unrealized holding gains 7,246 13,906
Available-for-sale debt securities:    
Total available-for-sale debt securities, fair value 62,670 60,160
Total available-for-sale debt securities, gross unrealized gains 21,979 15,311
Total available-for-sale debt securities, gross unrealized losses (727) (292)
Available-for-sale equities securities    
Available-for-sale equity securities - energy industry 131,250 139,858
Available-for-sale equity securities, gross unrealized holding gains 46,780 53,487
Available-for-sale equity securities, gross unrealized holding losses (745) (2,566)
Total short-term investments 144,220 159,488
Total short-term investments, gross unrealized gains 54,026 67,393
Total short-term investments, gross unrealized losses (745) (2,566)
Total cash, cash equivalents and short-term investments, fair value 673,042 801,190
Total cash, cash equivalents and short-term investments, gross unrealized gains 54,026 67,393
Total cash, cash equivalents and short-term investments, gross unrealized losses (745) (2,566)
Equity Securities [Member]
   
Available-for-sale equities securities    
Available-for-sale equity securities - energy industry 68,580 79,698
Available-for-sale equity securities, gross unrealized holding gains 24,801 38,176
Available-for-sale equity securities, gross unrealized holding losses (18) (2,274)
Commercial paper and CDs [Member]
   
Available-for-sale debt securities:    
Total available-for-sale debt securities, fair value 1,216 1,275
Corporate debt securities [Member]
   
Available-for-sale debt securities:    
Total available-for-sale debt securities, fair value 55,300 52,022
Total available-for-sale debt securities, gross unrealized gains 21,944 15,274
Total available-for-sale debt securities, gross unrealized losses   (18)
Available-for-sale equities securities    
Available-for-sale equity securities, gross unrealized holding losses (479)  
Mortgage-backed debt securities [Member]
   
Available-for-sale debt securities:    
Total available-for-sale debt securities, fair value 370 372
Total available-for-sale debt securities, gross unrealized gains 19 16
Mortgage-CMO debt securities [Member]
   
Available-for-sale debt securities:    
Total available-for-sale debt securities, fair value 2,754 3,015
Total available-for-sale debt securities, gross unrealized gains 16 21
Total available-for-sale debt securities, gross unrealized losses (99) (6)
Asset-backed debt securities [Member]
   
Available-for-sale debt securities:    
Total available-for-sale debt securities, fair value 3,030 3,476
Total available-for-sale debt securities, gross unrealized losses $ (149) $ (268)