GOODWILL AND OTHER INTANGIBLE ASSETS (Details) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2011	Jun. 30, 2011	Dec. 31, 2010
Changes to goodwill
Balance at the beginning of the period		$ 60,252,000
Acquired from acquisitions		27,062,000
Foreign currency translation		1,197,000
Balance at the end of the period	88,511,000	88,511,000	60,252,000
Finite-lived intangible assets
Cost	194,103,000	194,103,000	175,033,000
Accumulated Amortization	67,035,000	67,035,000	60,633,000
Net	127,068,000	127,068,000	114,400,000
Weighted Average Amortization Period (in years)		9.4	9.7
Aggregate amortization expense	2,900,000	5,800,000
Permits
Finite-lived intangible assets
Cost	105,748,000	105,748,000	103,493,000
Accumulated Amortization	44,464,000	44,464,000	42,430,000
Net	61,284,000	61,284,000	61,063,000
Weighted Average Amortization Period (in years)		17.7	15.9
Customer relationships
Finite-lived intangible assets
Cost	69,781,000	69,781,000	58,322,000
Accumulated Amortization	14,008,000	14,008,000	10,418,000
Net	55,773,000	55,773,000	47,904,000
Weighted Average Amortization Period (in years)		7.0	8.0
Other intangible assets
Finite-lived intangible assets
Cost	18,574,000	18,574,000	13,218,000
Accumulated Amortization	8,563,000	8,563,000	7,785,000
Net	$ 10,011,000	$ 10,011,000	$ 5,433,000
Weighted Average Amortization Period (in years)		4.1	3.5