Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Statement Of Financial Position [Abstract]
Oil and natural gas properties, accumulated depreciation, depletion and amortization	$ 475,543	$ 389,206
Other property, accumulated depreciation and amortization	$ 714	$ 598
Common unitholders, units issued	42,599,080	42,320,707
Common unitholders, units outstanding	42,599,080	42,320,707