Segment Information (Details) $ in Millions	3 Months Ended
	Mar. 29, 2020 USD ($) segment	Mar. 31, 2019 USD ($)	Dec. 29, 2019 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment	2
Number of reportable segments | segment	2
Segment Information
Revenues	$ 366.6	$ 357.2
Operating expenses:
Cost of services (exclusive of depreciation and amortization)	231.0	218.4
Selling, general and administrative	38.0	33.6
Depreciation and amortization	22.5	21.8
Total operating expenses	291.5	273.8
Operating profit	75.1	83.4
Interest expense, net	16.0	9.7
Other expense, net	(0.7)	0.1
Income before income taxes	59.8	73.6
Income taxes	15.1	19.1
Net income	44.7	54.5
Total assets	2,215.5	2,016.6	$ 2,151.2
United States
Segment Information
Revenues	321.1	314.3
Operating expenses:
Cost of services (exclusive of depreciation and amortization)	198.0	189.1
Selling, general and administrative	35.1	30.0
Depreciation and amortization	20.8	20.0
Total operating expenses	253.9	239.1
Operating profit	67.2	75.2
Interest expense, net	16.1	9.7
Other expense, net	(0.1)	0.1
Income before income taxes	51.2	65.4
Income taxes	12.8	16.7
Net income	38.4	48.7
Total assets	2,036.4	1,812.5
International
Segment Information
Revenues	45.5	42.9
Operating expenses:
Cost of services (exclusive of depreciation and amortization)	33.0	29.3
Selling, general and administrative	2.9	3.6
Depreciation and amortization	1.7	1.8
Total operating expenses	37.6	34.7
Operating profit	7.9	8.2
Interest expense, net	(0.1)	0.0
Other expense, net	(0.6)	0.0
Income before income taxes	8.6	8.2
Income taxes	2.3	2.4
Net income	6.3	5.8
Total assets	$ 179.1	$ 204.1