Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Oil and natural gas properties, accumulated depreciation, depletion and amortization	$ 420,005	$ 389,206
Other property, accumulated depreciation and amortization	$ 636	$ 598
Common Unitholders [Member]
Common unitholders, units issued	42,599,080	42,320,707
Common unitholders, units outstanding	42,599,080	42,320,707