Segment Information Schedule of Assets Related to Balance Sheet (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Total assets	$ 5,968,136	$ 5,567,856
Gathering And Processing [Member]
Segment Reporting Information [Line Items]
Total assets	2,127,565	1,959,697
Joint Venture [Member]
Segment Reporting Information [Line Items]
Total assets	2,123,802	1,924,705
Contract Compression [Member]
Segment Reporting Information [Line Items]
Total assets	1,421,377	1,405,600
Contract Treating [Member]
Segment Reporting Information [Line Items]
Total assets	228,940	215,172
Corporate and Others [Member]
Segment Reporting Information [Line Items]
Total assets	$ 66,452	$ 62,682