QUARTERLY DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 858,204	$ 843,181	$ 849,140	$ 749,778	$ 747,403	$ 755,846	$ 752,788	$ 688,941	$ 3,300,303	$ 2,944,978	$ 2,755,226
Total cost of revenues	594,857	580,685	583,584	546,425	526,690	519,595	519,803	496,585	2,305,551	2,062,673	1,932,857
(Loss) income from operations	41,485	65,745	64,353	10,991	27,935	47,663	46,744	5,433	182,574	127,775	69,162
Other (expense) income, net	(4,061)	(996)	846	(299)	(3,305)	(432)	(833)	(1,549)	(4,510)	(6,119)	6,195
Net income (loss)	$ 16,431	$ 31,089	$ 30,747	$ (12,631)	$ 84,194	$ 12,058	$ 25,880	$ (21,393)	$ 65,636	$ 100,739	$ (39,873)
Basic (loss) earnings per share (in dollars per share)	$ 0.29	$ 0.55	$ 0.55	$ (0.22)	$ 1.48	$ 0.21	$ 0.45	$ (0.37)	$ 1.17	$ 1.77	$ (0.69)
Diluted (loss) earnings per share (in dollars per share)	$ 0.29	$ 0.55	$ 0.54	$ (0.22)	$ 1.48	$ 0.21	$ 0.45	$ (0.37)	$ 1.16	$ 1.76	$ (0.69)
Gain on sale of businesses							$ 31,700		$ 0	$ 30,732	$ 16,884
Loss on early extinguishment of debt		$ 2,500				$ 1,900	$ 6,000		$ 2,488	7,891	$ 0
Tax benefit due to reduction in net deferred tax liability					$ 93,000					$ 99,900