Severance, impairment and other associated costs (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jul. 01, 2011
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 10.6
Severance and related costs	10.4
Restructuring Reserve [Roll Forward]
Balance accrued at beginning of period	0.6
Net expense during the six months ended	10.4
Severance payments	(4.6)
Other associated costs	(0.1)
Balance accrued at end of period	6.3
North America Corporate Headquarters[Member]
Restructuring Cost and Reserve [Line Items]
Amount related to the transition and reorganization of corporate headquarters	2.6
Employees severed	30
Chinese Manufacturing plants [Member]
Restructuring Cost and Reserve [Line Items]
Severance and related costs	5.0
Write-down of manufacturing facility	0.2
Employees severed	1,800
Wireless Audio Components [Member]
Restructuring Cost and Reserve [Line Items]
Severance and related costs	$ 0.9
Employees severed	25