Segment Information - Revenues, Operating Income (Loss) and Assets by Reportable Segments (Details) - USD ($) $ 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
Segment Reporting Information [Line Items]
Total revenues	$ 206.4	$ 202.0	$ 170.4	$ 168.9	$ 185.1	$ 184.1	$ 187.9	$ 160.4	$ 747.7	$ 717.5	$ 618.0
Depreciation and amortization									24.6	23.4	17.9
Total operating income	9.0	$ 12.7	$ 2.9	$ 4.7	9.3	$ 11.5	$ 9.0	$ 8.2	29.3	38.0	30.5
Total assets	1,562.8				1,186.0				1,562.8	1,186.0	1,010.1
Discontinued operations
Segment Reporting Information [Line Items]
Total assets	0.0				3.3				0.0	3.3	8.3
Kratos Government Solutions
Segment Reporting Information [Line Items]
Total revenues									560.7	556.1
Unmanned Systems
Segment Reporting Information [Line Items]
Total revenues									187.0	161.4
Operating Segments | Kratos Government Solutions
Segment Reporting Information [Line Items]
Total revenues									560.7	556.1	485.1
Depreciation and amortization									17.9	18.2	13.2
Total operating income									43.6	45.2	35.5
Total assets	877.2				777.6				877.2	777.6	602.8
Operating Segments | Unmanned Systems
Segment Reporting Information [Line Items]
Total revenues									187.0	161.4	132.9
Depreciation and amortization									6.7	5.2	4.7
Total operating income									8.7	6.1	5.1
Total assets	292.4				246.3				292.4	246.3	220.9
Corporate activities
Segment Reporting Information [Line Items]
Total operating income									(23.0)	(13.3)	(10.1)
Total assets	$ 393.2				$ 158.8				393.2	158.8	178.1
Service revenues
Segment Reporting Information [Line Items]
Total revenues									248.7	272.6	200.7
Service revenues | Operating Segments | Kratos Government Solutions
Segment Reporting Information [Line Items]
Total revenues									248.7	272.6	200.7
Service revenues | Operating Segments | Unmanned Systems
Segment Reporting Information [Line Items]
Total revenues									0.0	0.0	0.0
Product sales
Segment Reporting Information [Line Items]
Total revenues									499.0	444.9	417.3
Product sales | Operating Segments | Kratos Government Solutions
Segment Reporting Information [Line Items]
Total revenues									312.0	283.5	284.4
Product sales | Operating Segments | Unmanned Systems
Segment Reporting Information [Line Items]
Total revenues									$ 187.0	$ 161.4	$ 132.9