Segment Information - Revenues, Operating Income (Loss) and Assets by Reportable Segments (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 25, 2016	Sep. 25, 2016	Jun. 26, 2016	Mar. 27, 2016	Dec. 27, 2015	Sep. 27, 2015	Jun. 28, 2015	Mar. 29, 2015	Dec. 25, 2016	Dec. 27, 2015	Dec. 28, 2014
Segment Reporting Information [Line Items]
Service revenues									$ 348.1	$ 354.2	$ 390.8
Product sales									320.6	302.9	372.2
Total revenues									668.7	657.1	763.0
Depreciation and amortization									22.8	25.5	32.4
Total operating income (loss) from continuing operations	$ 4.6	$ (13.0)	$ 0.0	$ (10.2)	$ 1.5	$ 1.6	$ (3.7)	$ (3.9)	(18.6)	(4.5)	5.3
Total assets	948.6				903.3				948.6	903.3	1,131.2
Discontinued operations
Segment Reporting Information [Line Items]
Total assets	0.0				0.0				0.0	0.0	190.8
Operating Segments | Kratos Government Solutions
Segment Reporting Information [Line Items]
Service revenues									221.0	209.5	207.4
Product sales									244.8	236.6	277.7
Total revenues									465.8	446.1	485.1
Depreciation and amortization									14.9	18.2	23.1
Total operating income (loss) from continuing operations									17.3	16.1	24.4
Total assets	609.8				606.8				609.8	606.8	618.9
Operating Segments | Public Safety & Security
Segment Reporting Information [Line Items]
Service revenues									127.1	144.7	183.4
Product sales									0.0	0.0	13.0
Total revenues									127.1	144.7	196.4
Depreciation and amortization									0.5	0.6	2.0
Total operating income (loss) from continuing operations									(3.0)	2.6	(4.9)
Total assets	92.0				96.8				92.0	96.8	100.2
Operating Segments | Unmanned Systems
Segment Reporting Information [Line Items]
Service revenues									0.0	0.0	0.0
Product sales									75.8	66.3	81.5
Total revenues									75.8	66.3	81.5
Depreciation and amortization									7.4	6.7	7.3
Total operating income (loss) from continuing operations									(27.7)	(16.2)	(9.8)
Total assets	172.1				162.0				172.1	162.0	166.1
Corporate activities
Segment Reporting Information [Line Items]
Total operating income (loss) from continuing operations									(5.2)	(7.0)	(4.4)
Total assets	$ 74.7				$ 37.7				$ 74.7	$ 37.7	$ 55.2