Business Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Segment Reporting Information [Line Items]
Number of Operating Segments			2
Revenues	$ 106,045	$ 106,951	$ 206,391	$ 158,924
Segment income (loss) before income taxes:	18,831	10,969	20,970	(26,556)
Assets held for sale	0		0		148,249	[1]
Total Assets	1,917,828		1,917,828		1,698,005	[1]
Oil and Gas Properties [Member]
Segment Reporting Information [Line Items]
Revenues	97,128	88,054	185,640	124,825
Segment income (loss) before income taxes:	45,101	39,623	73,728	25,579
Total Assets	1,841,382		1,841,382		1,461,130
Gas Marketing [Member]
Segment Reporting Information [Line Items]
Revenues	8,917	18,897	20,751	34,099
Segment income (loss) before income taxes:	156	690	498	899
Total Assets	9,888		9,888		14,713
Unallocated [Member]
Segment Reporting Information [Line Items]
Segment income (loss) before income taxes:	(26,426)	(29,344)	(53,256)	(53,034)
Total Assets	66,558		66,558		73,913
Assets Held for sale [Member]
Segment Reporting Information [Line Items]
Assets held for sale	$ 0		$ 0		$ 148,249

[1] Derived from audited 2011 balance sheet.