Other Assets - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017	Jan. 01, 2017	Sep. 30, 2018	Sep. 05, 2017
Business Acquisition [Line Items]
Intangible amortization expense	$ 1.8	$ 0.9	$ 0.6
Advances to PersolKelly Asia Pacific	7.0
Deferred sales commission	2.3
Teachers On Call, Inc.
Business Acquisition [Line Items]
Intangibles					$ 18.3
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
Finite-lived intangible assets, amortization expense, next 12 months	1.6
Finite-lived intangible assets, amortization expense, year 2	1.6
Finite-lived intangible assets, amortization expense, year 3	1.5
Finite-lived intangible assets, amortization expense, year 4	1.2
Finite-lived intangible assets, amortization expense, year 5	$ 1.2
Customer Relationships
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life	10 years
Customer Relationships | Teachers On Call, Inc.
Business Acquisition [Line Items]
Intangibles					12.0
Candidate Database
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life	4 years
Candidate Database | Teachers On Call, Inc.
Business Acquisition [Line Items]
Intangibles					1.5
Trademarks | Teachers On Call, Inc.
Business Acquisition [Line Items]
Intangibles					$ 4.8
Business Talent Group, LLC
Business Acquisition [Line Items]
Equity securities without readily determinable fair value, amount	$ 5.0			$ 5.0