Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012 item		Dec. 31, 2011		Dec. 31, 2010
Segment Information
Number of segments									3
Segment Information
Ownership interest (as a percent)	100.00%								100.00%
Segment information
Total segment gross margin									$ 287,106		$ 252,575		$ 227,389
Operations and maintenance expenses									77,943		65,326		53,487
Depreciation and amortization									77,104		69,156		62,572
Impairment									29,486		8,409
General and administrative expenses									50,648		48,680		40,347
Taxes other than income									7,392		5,130		4,726
Equity in (earnings) loss from unconsolidated affiliates									137,088		145,324		20,480
Gain on sale of operating assets									(9,941)
Operating (loss) income	(28,645)	43,185	35,530	(132,684)	20,302	(146,282)	20,178	16,352	(82,614)		(89,450)		45,777
Natural gas sales									360,340	[1]	452,726	[1]	381,453	[1]
Natural gas liquids sales									814,916		723,063		490,980
Transportation, compression and processing fees									192,270	[1],[2]	121,631	[1],[2]	68,398	[1],[2]
Condensate and other									50,194	[1]	47,803	[1]	54,333	[1]
Sales to external customers	396,796	366,393	317,303	337,228	355,551	353,691	346,056	289,925	1,417,720		1,345,223		995,164
Interest and other financing costs									55,264		47,187		53,605
Capital expenditures									359,340		273,293		130,504
Segment assets	2,200,164				2,064,597				2,200,164		2,064,597		1,906,993
Texas
Segment information
Total segment gross margin									204,324		184,437		128,682
Operations and maintenance expenses									47,352		38,099		29,236
Depreciation and amortization									38,289		28,934		24,696
Impairment											3,409
General and administrative expenses									12,585		13,208		9,966
Taxes other than income									4,523		2,436		2,191
Equity in (earnings) loss from unconsolidated affiliates									(34,734)		(10,853)		3,139
Gain on sale of operating assets									(9,941)
Operating (loss) income									146,250		109,204		59,454
Natural gas sales									234,752		278,235		188,588
Natural gas liquids sales									606,664		456,536		256,501
Transportation, compression and processing fees									148,470		92,846		43,233
Condensate and other									13,888		15,908		11,253
Sales to external customers									1,003,774		843,525		499,575
Capital expenditures									321,767		230,947		106,792
Segment assets	1,058,248				855,172				1,058,248		855,172		594,528
Oklahoma
Segment information
Total segment gross margin									88,468		105,080		93,617
Operations and maintenance expenses									30,334		26,982		23,955
Depreciation and amortization									35,145		35,726		33,154
Impairment									742
General and administrative expenses									9,126		9,094		8,655
Taxes other than income									2,841		2,659		2,503
Equity in (earnings) loss from unconsolidated affiliates									(1,104)		(2,415)		(2,840)
Operating (loss) income									11,384		33,034		28,190
Natural gas sales									125,509		180,032		197,632
Natural gas liquids sales									208,781		293,354		236,781
Transportation, compression and processing fees									27,778		11,832		7,336
Condensate and other									40,517		37,216		32,462
Sales to external customers									402,585		522,434		474,211
Capital expenditures									30,859		40,299		23,320
Segment assets	632,475				658,486				632,475		658,486		658,729
Rocky Mountains
Segment information
Total segment gross margin									932		2,641		4,440
Operations and maintenance expenses									257		245		296
Depreciation and amortization									2,068		3,061		3,061
Impairment									28,744		5,000
General and administrative expenses									1,619		1,415		1,775
Taxes other than income									18		18		27
Equity in (earnings) loss from unconsolidated affiliates									172,926		158,592		20,181
Operating (loss) income									(204,700)		(165,690)		(20,900)
Natural gas sales									79		475		1,234
Transportation, compression and processing fees									16,022		16,953		17,829
Condensate and other									1,878		1,419		1,666
Sales to external customers									17,979		18,847		20,729
Capital expenditures											(12)		(14)
Segment assets	220,557				459,457				220,557		459,457		651,096
Rocky Mountains | Producer Services Business
Segment Information
Ownership interest (as a percent)	100.00%								100.00%
Total segments
Segment information
Total segment gross margin									293,724		292,158		226,739
Operations and maintenance expenses									77,943		65,326		53,487
Depreciation and amortization									75,502		67,721		60,911
Impairment									29,486		8,409
General and administrative expenses									23,330		23,717		20,396
Taxes other than income									7,382		5,113		4,721
Equity in (earnings) loss from unconsolidated affiliates									137,088		145,324		20,480
Gain on sale of operating assets									(9,941)
Operating (loss) income									(47,066)		(23,452)		66,744
Natural gas sales									360,340		458,742		387,454
Natural gas liquids sales									815,445		749,890		493,282
Transportation, compression and processing fees									192,270		121,631		68,398
Condensate and other									56,283		54,543		45,381
Sales to external customers									1,424,338		1,384,806		994,515
Capital expenditures									352,626		271,234		130,098
Segment assets	1,911,280				1,973,115				1,911,280		1,973,115		1,904,353
Corporate and Other
Segment information
Total segment gross margin									(6,618)		(39,583)		650
Depreciation and amortization									1,602		1,435		1,661
General and administrative expenses									27,318		24,963		19,951
Taxes other than income									10		17		5
Operating (loss) income									(35,548)		(65,998)		(20,967)
Natural gas sales											(6,016)		(6,001)
Natural gas liquids sales									(529)		(26,827)		(2,302)
Condensate and other									(6,089)		(6,740)		8,952
Sales to external customers									(6,618)		(39,583)		649
Interest and other financing costs									55,264		47,187		53,605
Capital expenditures									6,714		2,059		406
Segment assets	$ 288,884				$ 91,482				$ 288,884		$ 91,482		$ 2,640

[1] Inclusive of related party transactions discussed in Note 7.

[2] Inclusive of the following affiliate transactions discussed in Note 7: Transportation, compression and processing fees $17,874 $2,091 $11 Cost of natural gas and natural gas liquids $171,138 $19,290 $518 Transportation $9,514 $6,846 $5,478