GOODWILL AND OTHER INTANGIBLE ASSETS (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2012 Y	Mar. 31, 2011	Dec. 31, 2011 Y
Finite-lived intangible assets
Cost	$ 215,956,000		$ 212,188,000
Accumulated Amortization	76,989,000		72,544,000
Net	138,967,000		139,644,000
Weighted Average Amortization Period (in years)	8.8		10.0
Aggregate amortization expense	3,900,000	2,900,000
Permits
Finite-lived intangible assets
Cost	107,894,000		106,939,000
Accumulated Amortization	46,743,000		45,629,000
Net	61,151,000		61,310,000
Weighted Average Amortization Period (in years)	16.7		17.9
Customer relationships
Finite-lived intangible assets
Cost	84,776,000		83,721,000
Accumulated Amortization	20,036,000		17,650,000
Net	64,740,000		66,071,000
Weighted Average Amortization Period (in years)	7.6		7.9
Other intangible assets
Finite-lived intangible assets
Cost	23,286,000		21,528,000
Accumulated Amortization	10,210,000		9,265,000
Net	$ 13,076,000		$ 12,263,000
Weighted Average Amortization Period (in years)	5.0		5.3