Goodwill and Intangible Assets - Goodwill (Details) - USD ($) $ in Millions	Oct. 01, 2017	Dec. 25, 2016
Goodwill [Line Items]
Gross value	$ 732.7	$ 732.8
Less accumulated impairment	247.4	247.4
Net	485.3	485.4
Kratos Government Solutions
Goodwill [Line Items]
Gross value	567.7	567.8
Less accumulated impairment	215.3	215.3
Net	352.4	352.5
Public Safety & Security
Goodwill [Line Items]
Gross value	53.9	53.9
Less accumulated impairment	18.3	18.3
Net	35.6	35.6
Unmanned Systems
Goodwill [Line Items]
Gross value	111.1	111.1
Less accumulated impairment	13.8	13.8
Net	$ 97.3	$ 97.3