Annual report pursuant to Section 13 and 15(d)

Commitments (Details)

v2.4.0.6
Commitments (Details) (USD $)
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Operating Leased Assets [Line Items]      
Minimum future lease payments due under noncancelable operating leases, 2012 $ 300,000    
Minimum future lease payments due under noncancelable operating leases, 2013 1,200,000    
Minimum future lease payments due under noncancelable operating leases, 2014 1,100,000    
Minimum future lease payments due under noncancelable operating leases, thereafter 10,000,000    
Total rent expense 1,900,000 2,000,000 2,200,000
Additional security requirements for 2012 0    
Additional security requirements for 2013 9,000,000    
Additional security requirements for 2014 9,000,000    
Additional security requirements for 2015 9,000,000    
Additional security requirements 2016 to 2023 30,000,000    
Drilling Rig Commitments [Member]
     
Operating Leased Assets [Line Items]      
Minimum future lease payments due under noncancelable operating leases, 2012 32,100,000    
Minimum future lease payments due under noncancelable operating leases, 2013 $ 1,700,000