Derivative Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Other Assets [Member]
Notional amounts and estimated fair values of outstanding derivative positions
Derivative assets, Estimated Fair Value	$ 3,424
Other Liabilities [Member]
Notional amounts and estimated fair values of outstanding derivative positions
Derivative liabilities, Estimated Fair Value	1,658
Oil [Member]
Notional amounts and estimated fair values of outstanding derivative positions
Notional Units	Barrels
Derivative assets, Notional Amount	877
Derivative assets, Estimated Fair Value	2,174
Derivative liabilities, Notional Amount	(877)
Derivative liabilities, Estimated Fair Value	(1,215)
Natural Gas [Member]
Notional amounts and estimated fair values of outstanding derivative positions
Notional Units	MMBTUs
Derivative assets, Notional Amount	4,653
Derivative assets, Estimated Fair Value	1,250
Derivative liabilities, Notional Amount	(4,653)
Derivative liabilities, Estimated Fair Value	$ (443)