Oil and Gas Operations (Unaudited) (Oil and Gas Operations) (Details)	12 Months Ended
	Dec. 31, 2013 MMBoe	Dec. 31, 2012 MMBoe	Dec. 31, 2011 MMBoe
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved reserves at beginning of period, total	346.4	343.1	302.9
Revisions of previous estimates, total	4.6	(42.1)	(5.8)
Purchases, total	0.2	12.4	20.8
Extensions and discoveries, total	36.8	57.1	45.6
Production, total	(25.4)	(24.1)	(20.4)
Sales, total	(14.8)
Proved reserves at end of period, total	347.8	346.4	343.1
Proved developed reserves at end of period (BOE)	259.8	260.5	248.5
Proved undeveloped reserves at end of period (BOE)	88.0	85.9	94.6
Natural Gas Reserves
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved reserves at beginning of period	809,128	957,368	954,387
Revisions of previous estimates	18,465	(143,704)	(12,823)
Purchases	282	10,656	19,362
Extensions and discoveries	50,568	61,170	68,160
Production	(70,506)	(76,362)	(71,718)
Sales	(88,212)
Proved reserves at end of period	719,725	809,128	957,368
Proved developed reserves at end of period (volume)	623,305	708,657	788,812
Proved undeveloped reserves at end of period (volume)	96,420	100,471	168,556
Oil Reserves
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved reserves at beginning of period	155,348	129,578	103,262
Revisions of previous estimates	(680)	(8,546)	(4,513)
Purchases	142	7,950	12,583
Extensions and discoveries	20,517	35,132	24,564
Production	(10,378)	(8,766)	(6,318)
Sales	(79)
Proved reserves at end of period	164,870	155,348	129,578
Proved developed reserves at end of period (volume)	113,795	105,976	83,899
Proved undeveloped reserves at end of period (volume)	51,075	49,372	45,679
Natural Gas Liquids Reserves
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved reserves at beginning of period	56,155	53,957	40,601
Revisions of previous estimates	2,211	(9,557)	841
Purchases	56	2,569	5,055
Extensions and discoveries	7,823	11,759	9,637
Production	(3,233)	(2,573)	(2,177)
Sales	(1)
Proved reserves at end of period	63,011	56,155	53,957
Proved developed reserves at end of period (volume)	42,087	36,440	33,154
Proved undeveloped reserves at end of period (volume)	20,924	19,715	20,803