SEC defined prices (Details 2)	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	May 01, 2015	Apr. 01, 2015
NYMEX Oil Price [Member]
SEC Defined Pricing [Line Items]
SEC Defined Prices	82.72	94.99	99.08	100.27
Henry Hub Gas Price [Member]
SEC Defined Pricing [Line Items]
SEC Defined Prices	3.87	4.34	4.24	4.10
Ventura Gas Price [Member]
SEC Defined Pricing [Line Items]
SEC Defined Prices	3.96	7.71	7.60	7.47
Subsequent event [Member] | NYMEX Oil Price [Member]
SEC Defined Pricing [Line Items]
SEC Defined Prices					59.15	50.09
Subsequent event [Member] | Henry Hub Gas Price [Member]
SEC Defined Pricing [Line Items]
SEC Defined Prices					2.57	2.63
Subsequent event [Member] | Ventura Gas Price [Member]
SEC Defined Pricing [Line Items]
SEC Defined Prices					2.51	2.45