Segment Information - Revenues, Operating Income (Loss) and Assets by Reportable Segments (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Oct. 01, 2017	Jun. 25, 2017	Mar. 26, 2017	Dec. 25, 2016	Sep. 25, 2016	Jun. 26, 2016	Mar. 27, 2016	Dec. 31, 2017	Dec. 25, 2016	Dec. 27, 2015
Segment Reporting Information [Line Items]
Service revenues									$ 346.4	$ 348.1	$ 354.2
Product sales									405.5	320.6	302.9
Total revenues									751.9	668.7	657.1
Depreciation and amortization									22.5	22.8	25.5
Total operating loss from continuing operations	$ (13.2)	$ 3.1	$ 2.6	$ 1.7	$ 4.6	$ (13.0)	$ 0.0	$ (10.2)	(5.8)	(18.6)	(4.5)
Total assets	1,024.0				948.6				1,024.0	948.6	903.3
Operating Segments | Kratos Government Solutions
Segment Reporting Information [Line Items]
Service revenues									196.5	221.0	209.5
Product sales									283.8	244.8	236.6
Total revenues									480.3	465.8	446.1
Depreciation and amortization									14.3	14.9	18.2
Total operating loss from continuing operations									1.7	17.3	16.1
Total assets	597.9				609.8				597.9	609.8	606.8
Operating Segments | Public Safety & Security
Segment Reporting Information [Line Items]
Service revenues									149.9	127.1	144.7
Product sales									0.0	0.0	0.0
Total revenues									149.9	127.1	144.7
Depreciation and amortization									0.4	0.5	0.6
Total operating loss from continuing operations									3.8	(3.0)	2.6
Total assets	97.4				92.0				97.4	92.0	96.8
Operating Segments | Unmanned Systems
Segment Reporting Information [Line Items]
Service revenues									0.0	0.0	0.0
Product sales									121.7	75.8	66.3
Total revenues									121.7	75.8	66.3
Depreciation and amortization									7.8	7.4	6.7
Total operating loss from continuing operations									(3.0)	(27.7)	(16.2)
Total assets	201.9				172.1				201.9	172.1	162.0
Corporate activities
Segment Reporting Information [Line Items]
Total operating loss from continuing operations									(8.3)	(5.2)	(7.0)
Total assets	$ 126.8				$ 74.7				$ 126.8	$ 74.7	$ 37.7