GOODWILL AND OTHER INTANGIBLE ASSETS - Values of Intangible Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2013
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	$ 1,045,754	$ 1,024,567
Accumulated Amortization	136,251	114,922
Net Value	909,503	909,645	$ 720,035
Operating permits
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	238,517	247,933
Net Value	238,517	247,933
Tradenames
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	9,910	5,800
Net Value	9,910	5,800
Covenants not-to-compete
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	8,343	8,474
Accumulated Amortization	6,404	5,688
Net Value	1,939	2,786
Customer relationships
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	783,615	755,148
Accumulated Amortization	128,178	107,365
Net Value	655,437	647,783
Tradenames
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	4,257	6,062
Accumulated Amortization	1,004	1,313
Net Value	3,253	4,749
Technology
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	611	611
Accumulated Amortization	601	521
Net Value	10	90
Other
Intangible Assets by Major Class [Line Items]
Gross Carrying Amount	501	539
Accumulated Amortization	64	35
Net Value	$ 437	$ 504