Derivatives (Details 1) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Derivatives, Fair Value [Line Items]
Commodity derivative assets	$ 13,491	$ 25,356	$ 0
Commodity derivative liabilities	(1,480)	0	58,195
Commodity derivative assets - current	115,924	49,826	39,860
Commodity derivative assets - noncurrent	1,934	412	2,990
Commodity derivative liabilities - current	(43,183)	(37,387)	(42,622)
Commodity derivative liabilities - noncurrent	(2,182)	(1,063)	(2,177)
Commodity
Derivatives, Fair Value [Line Items]
Commodity derivative assets	142,608	52,432	59,476
Commodity derivative liabilities	(107,887)	(43,652)	(110,432)
Cash collateral	37,772	3,008	49,007
Total	72,493	11,788	(1,949)
Commodity derivative assets - current | Commodity
Derivatives, Fair Value [Line Items]
Commodity derivative assets	134,504	51,647	52,405
Commodity derivative liabilities	(56,832)	(4,829)	(61,552)
Cash collateral	38,252	3,008	49,007
Commodity derivative assets - current	115,924	49,826	39,860
Commodity derivative assets - noncurrent | Commodity
Derivatives, Fair Value [Line Items]
Commodity derivative assets	2,095	412	3,072
Commodity derivative liabilities	(161)	0	(82)
Cash collateral	0	0	0
Commodity derivative assets - noncurrent	1,934	412	2,990
Commodity derivative liabilities - current | Commodity
Derivatives, Fair Value [Line Items]
Commodity derivative assets	5,925	371	3,956
Commodity derivative liabilities	(48,628)	(37,758)	(46,578)
Cash collateral	(480)	0	0
Commodity derivative liabilities - current	(43,183)	(37,387)	(42,622)
Commodity derivative liabilities - noncurrent | Commodity
Derivatives, Fair Value [Line Items]
Commodity derivative assets	84	2	43
Commodity derivative liabilities	(2,266)	(1,065)	(2,220)
Cash collateral	0	0	0
Commodity derivative liabilities - noncurrent	$ (2,182)	$ (1,063)	$ (2,177)