Segment Information (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 28, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 28, 2020 USD ($) segment	Jun. 30, 2019 USD ($)	Dec. 29, 2019 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment			2
Number of reportable segments | segment			2
Segment Information
Revenues	$ 296.8	$ 366.4	$ 663.4	$ 723.6
Operating expenses:
Cost of services (exclusive of depreciation and amortization)	185.1	227.7	416.1	446.1
Selling, general and administrative	34.3	33.7	72.3	67.3
Depreciation and amortization	19.6	22.1	42.1	43.9
Total operating expenses	239.0	283.5	530.5	557.3
Operating profit	57.8	82.9	132.9	166.3
Interest expense, net	13.8	11.9	29.8	21.6
Other expense (income), net	0.1	(0.2)	(0.6)	(0.1)
Income before income taxes	43.9	71.2	103.7	144.8
Income taxes	10.7	19.9	25.8	39.0
Net income	33.2	51.3	77.9	105.8
Total assets	2,273.5	2,010.3	2,273.5	2,010.3	$ 2,151.2
United States
Segment Information
Revenues	265.9	320.5	587.0	634.8
Operating expenses:
Cost of services (exclusive of depreciation and amortization)	162.4	195.8	360.4	384.9
Selling, general and administrative	32.9	30.7	68.0	60.7
Depreciation and amortization	18.0	20.5	38.8	40.5
Total operating expenses	213.3	247.0	467.2	486.1
Operating profit	52.6	73.5	119.8	148.7
Interest expense, net	13.8	11.9	29.9	21.6
Other expense (income), net	0.0	(0.1)	(0.1)	0.0
Income before income taxes	38.8	61.7	90.0	127.1
Income taxes	11.0	17.3	23.8	34.0
Net income	27.8	44.4	66.2	93.1
Total assets	2,084.7	1,829.0	2,084.7	1,829.0
International
Segment Information
Revenues	30.9	45.9	76.4	88.8
Operating expenses:
Cost of services (exclusive of depreciation and amortization)	22.7	31.9	55.7	61.2
Selling, general and administrative	1.4	3.0	4.3	6.6
Depreciation and amortization	1.6	1.6	3.3	3.4
Total operating expenses	25.7	36.5	63.3	71.2
Operating profit	5.2	9.4	13.1	17.6
Interest expense, net	0.0	0.0	(0.1)	0.0
Other expense (income), net	0.1	(0.1)	(0.5)	(0.1)
Income before income taxes	5.1	9.5	13.7	17.7
Income taxes	(0.3)	2.6	2.0	5.0
Net income	5.4	6.9	11.7	12.7
Total assets	$ 188.8	$ 181.3	$ 188.8	$ 181.3