QUARTERLY DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 871,005	$ 891,668	$ 868,678	$ 780,839	$ 858,204	$ 843,181	$ 849,140	$ 749,778	$ 3,412,190	$ 3,300,303	$ 2,944,978
Total cost of revenues	615,768	612,754	594,933	564,364	594,857	580,685	583,584	546,425	2,387,819	2,305,551	2,062,673
Income from operations	52,307	80,367	73,048	23,734	41,485	65,745	64,353	10,991	229,456	182,574	127,775
Other income (expense), net	905	(427)	(564)	2,983	(4,061)	(996)	846	(299)	2,897	(4,510)	(6,119)
Net income	$ 24,151	$ 36,369	$ 36,244	$ 976	$ 16,431	$ 31,089	$ 30,747	$ (12,631)	$ 97,740	$ 65,636	$ 100,739
Basic (loss) earnings per share (in dollars per share)	$ 0.43	$ 0.65	$ 0.65	$ 0.02	$ 0.29	$ 0.55	$ 0.55	$ (0.22)	$ 1.75	$ 1.17	$ 1.77
Diluted (loss) earnings per share (in dollars per share)	$ 0.43	$ 0.65	$ 0.65	$ 0.02	$ 0.29	$ 0.55	$ 0.54	$ (0.22)	$ 1.74	$ 1.16	$ 1.76
Loss on early extinguishment of debt		$ 6,100				$ 2,500			$ 6,131	$ 2,488	$ 7,891