SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Intangible Assets Amortization (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Intangible Assets
Original Cost	$ 71,020	$ 47,283
Accumulated Amortization	(44,378)	(26,737)
Intangibles, Net	26,642	20,546
Estimated amortization expense attributable to intangible assets
2017	10,581
2018	6,830
2019	7,737
2020	391
2021	74
Thereafter	1,029
Noncompete agreement
Intangible Assets
Original Cost	14,542	14,729
Accumulated Amortization	(10,974)	(9,750)
Intangibles, Net	3,568	4,979
Customer contracts and other, net
Intangible Assets
Original Cost	54,978	31,054
Accumulated Amortization	(33,300)	(16,959)
Intangibles, Net	21,678	14,095
Permits
Intangible Assets
Original Cost	1,500	1,500
Accumulated Amortization	(104)	(28)
Intangibles, Net	$ 1,396	$ 1,472