Derivative Instruments Derivative instruments (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) bbl MMBTU	Dec. 31, 2014 bbl MMBTU	Mar. 31, 2013 USD ($)
Derivative instruments [Line Items]
Amount of unrealized gain (loss) on hedge at de-designation date to be reclassified into AOCI			$ 1,800,000
Cash flow hedge gain (loss) to be reclassified within twelve months from AOCI into earnings	$ (400,000)
Oil swap and or collar [Member]
Derivative instruments [Line Items]
Derivative, nonmonetary notional amount | bbl	0	270,000
Natural gas swap or and collar [Member]
Derivative instruments [Line Items]
Derivative, nonmonetary notional amount | MMBTU	0	5,000,000