Quarterly Financial Data (Unaudited) Summarized Quarterly 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
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 206.4	$ 202.0	$ 170.4	$ 168.9	$ 185.1	$ 184.1	$ 187.9	$ 160.4	$ 747.7	$ 717.5	$ 618.0
Gross profit	54.3	57.1	46.0	45.8	48.4	48.6	48.1	44.9	203.2	190.0	169.7
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
Provision (benefit) for income taxes	(75.3)	5.0	(1.8)	(1.4)	1.0	2.8	2.5	(1.5)	(73.5)	4.8	4.6
Income (loss) from continuing operations	78.1	2.6	(0.6)	0.2	3.3	2.6	1.3	3.7
Income (loss) from discontinued operations	(0.1)	(0.2)	(0.2)	(0.4)	(0.7)	0.0	3.0	(0.6)
Net income (loss)	78.0	2.4	(0.8)	(0.2)	2.6	2.6	4.3	3.1	79.4	12.6	(3.5)
Less: Net loss attributable to noncontrolling interest	(0.1)	0.0	(0.1)	0.0	(0.4)	0.1	0.4	0.0	(0.2)	0.1	0.0
Net income (loss) 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)
Basic income (loss) per common share attributable to Kratos:
Income (loss) from continuing operations (in dollars per share)	$ 0.63	$ 0.02	$ (0.01)	$ 0	$ 0.03	$ 0.02	$ 0.01	$ 0.04	$ 0.70	$ 0.10	$ 0.04
Income (loss) from discontinued operations (in dollars per share)	0	0	0	0	0	0	0.03	(0.01)	(0.01)	0.02	(0.07)
Net income (loss) per common share (in dollars per share)	0.63	0.02	(0.01)	0	0.03	0.02	0.04	0.03	0.69	0.12	(0.03)
Diluted income (loss) per common share attributable to Kratos:
Income (loss) from continuing operations (in dollars per share)	0.62	0.02	(0.01)	0	0.03	0.02	0.01	0.03	0.68	0.10	0.04
Income from discontinued operations (in dollars per share)	0	0	0	0	0	0	0.03	0	(0.01)	0.01	(0.07)
Net income (loss) per common share (in dollars per share)	$ 0.62	$ 0.02	$ (0.01)	$ 0	$ 0.03	$ 0.02	$ 0.04	$ 0.03	$ 0.67	$ 0.11	$ (0.03)