Severance, impairment and other associated costs (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 29, 2013	Mar. 30, 2012
Restructuring Reserve [Roll Forward]
Balance accrued at beginning of period	$ 0.7
Net expense	0
Cash payments	(0.5)
Non-cash charges	0.2
Balance accrued at end of period	0.4
Restructuring charges	0.1	1.5
Workforce reduction		0.6
Accrual for restructuring actions	0.4
Chinese Manufacturing plants [Member]
Restructuring Reserve [Roll Forward]
Severance and related costs		0.7
Wireless Audio Components [Member]
Restructuring Reserve [Roll Forward]
Other restructuring costs		$ 0.2