Fair Value Measurement (Details) (Fair Value Measurements Recurring [Member], USD $) In Thousands	Jun. 30, 2011
Fair Value Line Items [Abstract]
Commodity derivatives	$ 9
Long-term investments	1,027
Total	1,036
Commodity derivatives	34,118
Interest-rate swap derivatives	34,392
Total	68,510
Level 1 [Member]
Fair Value Line Items [Abstract]
Commodity derivatives	0
Long-term investments	1,027
Total	1,027
Commodity derivatives	0
Interest-rate swap derivatives	0
Total	0
Level 2 [Member]
Fair Value Line Items [Abstract]
Commodity derivatives	9
Long-term investments	0
Total	9
Commodity derivatives	34,118
Interest-rate swap derivatives	34,392
Total	68,510
Level 3 [Member]
Fair Value Line Items [Abstract]
Commodity derivatives	0
Long-term investments	0
Total	0
Commodity derivatives	0
Interest-rate swap derivatives	0
Total	$ 0