Description of business and summary of significant accounting policies - Additional Information (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 27, 2015	Jun. 28, 2015	Mar. 29, 2015	Dec. 28, 2014	Sep. 28, 2014	Jun. 29, 2014	Mar. 30, 2014	Dec. 29, 2013	Sep. 27, 2015	Sep. 28, 2014	Sep. 29, 2013
Basis of Presentation [Line Items]
Stock awards excluded from computation of diluted EPS									0.2	2.8	1.8
Net income	$ 25.3	$ 14.7	$ 24.9	$ 19.7	$ 32.8	$ (4.3)	$ (6.8)	$ 1.4	$ 84.6	$ 23.1	$ 43.7
Debt Issuance Cost									$ 11.7	$ 4.7
International
Basis of Presentation [Line Items]
Percentage of net sales from international market									51.00%		47.00%
Defense And Security
Basis of Presentation [Line Items]
Concentration of credit risk in major customer									27.00%
Internal Revenue Service (IRS) | Minimum
Basis of Presentation [Line Items]
Open tax years by major tax jurisdiction									2007
Internal Revenue Service (IRS) | Maximum
Basis of Presentation [Line Items]
Open tax years by major tax jurisdiction									2014
Foreign Country | Minimum
Basis of Presentation [Line Items]
Open tax years by major tax jurisdiction									2011
Foreign Country | Maximum
Basis of Presentation [Line Items]
Open tax years by major tax jurisdiction									2014