SEGMENT INFORMATION - External Customer Revenue by Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 29, 2019	Sep. 29, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 30, 2018	Sep. 30, 2018	Jul. 01, 2018	Apr. 01, 2018	Dec. 29, 2019	Dec. 30, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenue from services	$ 591,040	$ 636,793	$ 588,594	$ 552,352	$ 650,147	$ 680,371	$ 614,301	$ 554,388	$ 2,368,779	$ 2,499,207	$ 2,508,771
Revenue from sales, percent									100.00%	100.00%	100.00%
United States
Segment Reporting Information [Line Items]
Revenue from services									$ 2,222,543	$ 2,369,024	$ 2,387,992
Revenue from sales, percent									93.80%	94.80%	95.20%
International operations
Segment Reporting Information [Line Items]
Revenue from services									$ 146,236	$ 130,183	$ 120,779
Revenue from sales, percent									6.20%	5.20%	4.80%