Derivative Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Asset derivatives:
Derivative instruments, at fair value	$ 79,821	$ 107,647
Liability derivatives:
Derivative instruments, at fair value	59,333	29,651
Margin deposits received (remitted to) counterparties	(100)	(300)
Commodity derivatives
Asset derivatives:
Derivative instruments, at fair value	79,821	107,647
Derivative instruments subject to master netting agreements	(26,095)	(20,843)
Derivative instruments, net	53,726	86,804
Liability derivatives:
Derivative instruments, at fair value	59,333	29,651
Derivative instruments subject to master netting agreements	(26,095)	(20,843)
Margin deposits received (remitted to) counterparties	(53)	(266)
Derivative instruments, net	$ 33,185	$ 8,542