Annual report pursuant to Section 13 and 15(d)

重要会计政策摘要（叙述性）（详情）

v2.4.0.6
重大会计政策摘要（叙述性）（详情）（美元）
 12 Months Ended
Dec. 31, 2012
purchaser
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Summary Of Significant Accounting Policies [Line Items]        
Number Of Purchasers 2      
Accounts receivable, collection period 30 days      
Conversion ratio, gas to barrels of oil 6      
不包括摊销的石油和天然气资产的资本化成本 $ 626,295,000 $ 138,623,000    
Gas balancing payable 354,000 0    
Cumulative transaltion adjustment $ 2,442,000 $ 1,087,000 $ 2,952,000 $ 696,000
Minimum [Member]
        
Summary Of Significant Accounting Policies [Line Items]        
Useful life 3 years      
Maximum [Member]
        
Summary Of Significant Accounting Policies [Line Items]        
Useful life 30 years