GOODWILL AND OTHER INTANGIBLE ASSETS (Details) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Y	Jun. 30, 2011	Dec. 31, 2011 Y
Finite-lived intangible assets
Cost	$ 218,622,000		$ 218,622,000		$ 212,188,000
Accumulated Amortization	80,000,000		80,000,000		72,544,000
Net	138,622,000		138,622,000		139,644,000
Weighted Average Amortization Period (in years)			9.0		10.0
Aggregate amortization expense	3,500,000	2,900,000	7,300,000	5,800,000
Permits
Finite-lived intangible assets
Cost	109,273,000		109,273,000		106,939,000
Accumulated Amortization	47,481,000		47,481,000		45,629,000
Net	61,792,000		61,792,000		61,310,000
Weighted Average Amortization Period (in years)			16.7		17.9
Customer relationships
Finite-lived intangible assets
Cost	87,299,000		87,299,000		83,721,000
Accumulated Amortization	21,904,000		21,904,000		17,650,000
Net	65,395,000		65,395,000		66,071,000
Weighted Average Amortization Period (in years)			7.3		7.9
Other intangible assets
Finite-lived intangible assets
Cost	22,050,000		22,050,000		21,528,000
Accumulated Amortization	10,615,000		10,615,000		9,265,000
Net	$ 11,435,000		$ 11,435,000		$ 12,263,000
Weighted Average Amortization Period (in years)			3.7		5.3