GOODWILL AND OTHER INTANGIBLE ASSETS - Carrying Values of Other Intangible Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	$ 2,180,894	$ 2,133,541
Accumulated Amortization	362,816	271,568
Net Value	1,818,078	1,861,973	$ 1,842,561
Operating permits
Intangible Assets By Major Class [Line Items]
Carrying Amount, Indefinite Lived Intangible Assets	231,819	229,396
Tradenames
Intangible Assets By Major Class [Line Items]
Carrying Amount, Indefinite Lived Intangible Assets	317,193	316,472
Customer relationships
Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	1,600,141	1,553,398
Accumulated Amortization	352,140	261,306
Net Value	1,248,001	1,292,092
Covenants not-to-compete
Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	7,899	9,491
Accumulated Amortization	5,674	6,371
Net Value	2,225	3,120
Tradenames
Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	5,988	5,708
Accumulated Amortization	1,724	1,365
Net Value	4,264	4,343
Other
Intangible Assets By Major Class [Line Items]
Gross Carrying Amount	17,854	19,076
Accumulated Amortization	3,278	2,526
Net Value	$ 14,576	$ 16,550