Acquisition - Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 27, 2020	Sep. 27, 2020	Jun. 28, 2020	Mar. 29, 2020	Dec. 29, 2019	Sep. 29, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 27, 2020	Dec. 29, 2019	Dec. 30, 2018
Business Acquisition [Line Items]
Pro forma net income attributable to Kratos	$ 78.1	$ 2.4	$ (0.7)	$ (0.2)	$ 3.0	$ 2.5	$ 3.9	$ 3.1	$ 79.6	$ 12.5	$ (3.5)
FTT Inc
Business Acquisition [Line Items]
Pro forma revenues										725.6
Pro forma net income before tax										14.8
Pro forma net income										11.7
Pro forma net income attributable to Kratos										$ 11.8
Basic pro forma income per share attributable to Kratos (in dollars per share)										$ 0.11
Diluted pro forma income per share attributable to Kratos (in dollars per share)										$ 0.11
CPI ASC Signal Division, Inc.
Business Acquisition [Line Items]
Pro forma revenues									766.0
Pro forma net income before tax									2.6
Pro forma net income									$ (1.4)
Basic pro forma income per share attributable to Kratos (in dollars per share)									$ (0.01)
Diluted pro forma income per share attributable to Kratos (in dollars per share)									$ (0.01)