Annual report pursuant to Section 13 and 15(d)

Supplemental Oil and Gas Information - Changes in Standardized Measure of Discounted Future Net Cash Flows (Details)

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Supplemental Oil and Gas Information - Changes in Standardized Measure of Discounted Future Net Cash Flows (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2010
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Roll Forward]      
Standardized measure of discounted future net cash flows for Fiscal year ended $ 110,280 $ 85,354 $ 20,055
Net change in prices and production costs 18,517 24,937  
Extensions and discoveries 6,785 117 115,092
Acquisitions of reserves 31,456 3,486 29,656
Revisions of previous quantity estimates (31,702) [1] (5,947) (6,408)
Changes in estimated future development costs (2,830) (262)  
Divestiture of reserves     (11,687)
Sales and transfers of oil and gas produced (1,205) (4,346) (13,363)
Previously estimated development cost incurred during the period 5,841    
Accretion of discount 0 [2] 13,934 1,725
Net change in income taxes (3,233) (15,828) (51,495)
Net change in timing and other (3,834) 8,835 1,779
Standardized measure of discounted future net cash flows for Fiscal year ended 130,075 110,280 85,354
United States
      
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Roll Forward]      
Standardized measure of discounted future net cash flows for Fiscal year ended 110,016 85,208 0
Net change in prices and production costs 18,517 24,899  
Extensions and discoveries 6,785 117 115,092
Acquisitions of reserves 26,584 3,486 29,656
Revisions of previous quantity estimates (37,846) [1] (7,041) (8,258)
Changes in estimated future development costs (2,275) (798)  
Divestiture of reserves     0
Sales and transfers of oil and gas produced (941) (2,406) (1,064)
Previously estimated development cost incurred during the period 5,841    
Accretion of discount 0 [2] 13,893 1,725
Net change in income taxes (1,657) (16,125) (53,722)
Net change in timing and other (3,528) 8,783 1,779
Standardized measure of discounted future net cash flows for Fiscal year ended 121,496 110,016 85,208
Australia
      
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Roll Forward]      
Standardized measure of discounted future net cash flows for Fiscal year ended 264 146 20,055
Net change in prices and production costs 0 38  
Extensions and discoveries 0 0 0
Acquisitions of reserves 4,872 0 0
Revisions of previous quantity estimates 6,144 [1] 1,094 1,850
Changes in estimated future development costs (555) 536  
Divestiture of reserves     (11,687)
Sales and transfers of oil and gas produced (264) (1,940) (12,299)
Previously estimated development cost incurred during the period 0    
Accretion of discount 0 [2] 41 0
Net change in income taxes (1,576) 297 2,227
Net change in timing and other (306) 52 0
Standardized measure of discounted future net cash flows for Fiscal year ended $ 8,579 $ 264 $ 146
[1] The downward revision of previous quantity estimates of 1,644 Mbbls resulted from a reduced well count which was impacted by higher operating costs
[2] For the year ended June 30, 2012, Magellan assumed no benefit from the accretion of the beginning of year value of its proved oil reserves in the United States. Accretion, with respect to measuring the changes in the standardized measure of reserves values, represents the value benefit of being closer in time, relative to the prior year's standardized measure, to future cash flows in the reserves projections. During the year ended June 30, 2012, Magellan did not develop its United States proved oil reserves in accordance with its reserve plan as of June 30, 2011, and instead postponed its reserves development plan by one year. Therefore, the benefit of accretion of last year's reserves should not factor into the value of the current standardized measure.