Segment Information (Amounts Related To Balance Sheets For Each Segment) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Revenue from External Customers	$ 357,899	$ 317,252
Intersegment revenues	0	0
Total segment margin	118,246	100,991
Operation and maintenance	40,981	33,672
Gathering And Processing [Member]
Revenue from External Customers	307,167	265,972
Intersegment revenues	0	0
Total segment margin	71,335	53,800
Operation and maintenance	28,223	22,942
Corporate Joint Venture [Member]
Revenue from External Customers	0	0
Intersegment revenues	0	0
Total segment margin	0	0
Operation and maintenance	0	0
Contract Compression [Member]
Revenue from External Customers	37,201	38,436
Intersegment revenues	4,129	6,553
Total segment margin	38,986	41,440
Operation and maintenance	16,407	16,504
Contract Treating [Member]
Revenue from External Customers	9,135	8,433
Intersegment revenues	494	0
Total segment margin	7,883	7,251
Operation and maintenance	844	734
Corporate and Others [Member]
Revenue from External Customers	4,396	4,411
Intersegment revenues	56	67
Total segment margin	4,648	5,053
Operation and maintenance	113	45
Business Intersegment, Eliminations [Member]
Revenue from External Customers	0	0
Intersegment revenues	(4,679)	(6,620)
Total segment margin	(4,606)	(6,553)
Operation and maintenance	$ (4,606)	$ (6,553)