Commitments and contingencies (Details) (USD $)	12 Months Ended
	Dec. 28, 2012	Dec. 30, 2011	Dec. 31, 2010
Commitments and contingencies [Abstract]
Rental expense	$ 5,100,000	$ 6,300,000	$ 6,900,000
Aggregate minimum rental commitments under non-cancelable leases [Abstract]
2013	3,294,000
2014	2,326,000
2015	1,786,000
2016	1,234,000
2017	733,000
Thereafter	1,164,000
Total rent expense	10,537,000
Loss Contingencies [Line Items]
Number of patents infringed	3
Damage and interest payable amount	2,000,000
Increase in legal reserve	1,800,000	200,000
Contingent liability related to Halo	3,700,000
Legal expenses	1,200,000	800,000
Additional increase in legal reserve	$ 3,700,000
Pending or Threatened Litigation Halo [Member]
Loss Contingencies [Line Items]
Lawsuit filing date	March 2007
Domicile of Litigation	United States District Court, District of Nevada
Plaintiff allegations	The plaintiff, Halo, claims that we infringe certain U.S. patents related to an electronic surface mount package, and is seeking injunctive relief and damages.