Employee benefit plans (Details) (USD $)	12 Months Ended
	Dec. 28, 2012		Dec. 30, 2011		Dec. 31, 2010
Accumulated other comprehensive income for defined benefit plans [Abstract]
Pension cost expected to be amortized from accumulated other comprehensive income	$ 100,000		$ (800,000)		$ 1,100,000
Benefit obligations in excess of plan assets [Abstract]
Expected contributions to defined benefit plans in next fiscal year	1,100,000
Defined benefit plan expected future benefit payments Year 2019	6,200,000
Expected benefit payments [Abstract]
Defined contribution pension plan expense of non-U.S. subsidiaries	1,100,000		1,200,000		2,600,000
Contribution expense under 401(k) plans	900,000		1,000,000		300,000
Pension Plans [Member]
Net pension cost related to defined benefit plans [Abstract]
Service cost	0		38,000		296,000
Interest cost	1,685,000		1,811,000		1,860,000
Expected return on plan assets	(1,615,000)		(2,496,000)		(2,290,000)
Amortization of transition obligation	5,000		5,000		5,000
Amortization of prior service costs	1,000		3,000		17,000
Recognized actuarial losses (gains)	0		(26,000)		0
Curtailment gains	(18,000)		(152,000)		(1,031,000)
Special termination benefits	0		0		2,225,000
Net periodic pension cost (income)	58,000		(817,000)		1,082,000
Change in benefit obligation [Rollforward]
Projected benefit obligation at beginning of year	38,195,000		34,628,000
Service cost	0		38,000		296,000
Interest cost	1,685,000		1,811,000		1,860,000
Actuarial losses	2,969,000		3,699,000
Benefits paid	(2,152,000)		(1,934,000)
Plan curtailments	(61,000)		(47,000)
Projected benefit obligation at end of year	40,636,000		38,195,000		34,628,000
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at beginning of year	33,569,000	[1]	32,459,000
Actual return on plan assets	3,592,000		2,880,000
Employer contributions	108,000		164,000
Benefits paid	(2,152,000)		(1,934,000)
Fair value of plan assets at end of year	35,117,000	[1]	33,569,000	[1]	32,459,000
Amounts recognized on the Consolidated Balance Sheets [Abstract]
Non-current assets	235,000		181,000
Non-current liabilities	(5,754,000)		(4,807,000)
Net amount recorded	(5,519,000)		(4,626,000)
Accumulated benefit obligation	40,200,000		37,500,000
Accumulated other comprehensive income for defined benefit plans [Abstract]
Actuarial losses	(4,027,000)		(3,096,000)
Plan curtailment	(84,000)		(84,000)
Amortization of prior service costs	(20,000)		(21,000)
Amortization of transition obligations	(7,000)		(10,000)
Accumulated other comprehensive income	(4,138,000)		(3,211,000)
Benefit obligations in excess of plan assets [Abstract]
Projected benefit obligation	40,477,000		37,833,000
Accumulated benefit obligation	40,384,000		37,725,000
Plan assets	34,723,000		33,026,000
Asset category [Abstract]
Weighted-average asset allocations, Total (in hundredths)	100.00%		100.00%
Fair value of plan assets	35,117,000	[1]	33,569,000	[1]	32,459,000
Assumptions used to develop defined benefit plan [Abstract]
Discount rate (in hundredths)	4.10%		4.60%
Annual compensation increases (in hundredths)	0.00%		0.00%
Expected long-term rates of return on plan assets (in hundredths)	5.00%		8.00%
Expected benefit payments [Abstract]
2013	2,054,000
2014	2,055,000
2015	2,054,000
2016	2,137,000
2017	2,161,000
Thereafter	30,176,000
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	35,100,000	[1]	33,600,000	[1]
Asset category [Abstract]
Fair value of plan assets	35,100,000	[1]	33,600,000	[1]
Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	0	[1]	0	[1]
Asset category [Abstract]
Fair value of plan assets	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	0	[1]	0	[1]
Asset category [Abstract]
Fair value of plan assets	0	[1]	0	[1]
Equity Securities [Member] | Pension Plans [Member]
Asset category [Abstract]
Weighted-average asset allocations, Total (in hundredths)	11.00%		10.00%
Fixed Income Securities [Member] | Pension Plans [Member]
Asset category [Abstract]
Weighted-average asset allocations, Total (in hundredths)	89.00%		88.00%
Others [Member] | Pension Plans [Member]
Asset category [Abstract]
Weighted-average asset allocations, Total (in hundredths)	0.00%		2.00%
Cash and Cash Equivalents [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	100,000	[1]	100,000	[1]
Asset category [Abstract]
Fair value of plan assets	100,000	[1]	100,000	[1]
Cash and Cash Equivalents [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	100,000	[1]	100,000	[1]
Asset category [Abstract]
Fair value of plan assets	100,000	[1]	100,000	[1]
Cash and Cash Equivalents [Member] | Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	0	[1]	0	[1]
Asset category [Abstract]
Fair value of plan assets	0	[1]	0	[1]
Cash and Cash Equivalents [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	0	[1]	0	[1]
Asset category [Abstract]
Fair value of plan assets	0	[1]	0	[1]
Fixed Income Securities Corporate Bonds [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	30,800,000	[1],[2]	29,100,000	[1],[2]
Asset category [Abstract]
Fair value of plan assets	30,800,000	[1],[2]	29,100,000	[1],[2]
Fixed Income Securities Corporate Bonds [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	30,800,000	[1],[2]	29,100,000	[1],[2]
Asset category [Abstract]
Fair value of plan assets	30,800,000	[1],[2]	29,100,000	[1],[2]
Fixed Income Securities Corporate Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	0	[1],[2]	0	[1],[2]
Asset category [Abstract]
Fair value of plan assets	0	[1],[2]	0	[1],[2]
Fixed Income Securities Corporate Bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	0	[1],[2]	0	[1],[2]
Asset category [Abstract]
Fair value of plan assets	0	[1],[2]	0	[1],[2]
Fixed Income Securities Short-term Debt Securities [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	500,000	[1],[3]	1,000,000	[1],[3]
Asset category [Abstract]
Fair value of plan assets	500,000	[1],[3]	1,000,000	[1],[3]
Fixed Income Securities Short-term Debt Securities [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	500,000	[1],[3]	1,000,000	[1],[3]
Asset category [Abstract]
Fair value of plan assets	500,000	[1],[3]	1,000,000	[1],[3]
Fixed Income Securities Short-term Debt Securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	0	[1],[3]	0	[1],[3]
Asset category [Abstract]
Fair value of plan assets	0	[1],[3]	0	[1],[3]
Fixed Income Securities Short-term Debt Securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	0	[1],[3]	0	[1],[3]
Asset category [Abstract]
Fair value of plan assets	0	[1],[3]	0	[1],[3]
Equity Securities International Small-cap Value [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	1,100,000	[1],[4]	1,000,000	[1],[4]
Asset category [Abstract]
Fair value of plan assets	1,100,000	[1],[4]	1,000,000	[1],[4]
Equity Securities International Small-cap Value [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	1,100,000	[1],[4]	1,000,000	[1],[4]
Asset category [Abstract]
Fair value of plan assets	1,100,000	[1],[4]	1,000,000	[1],[4]
Equity Securities International Small-cap Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	0	[1],[4]	0	[1],[4]
Asset category [Abstract]
Fair value of plan assets	0	[1],[4]	0	[1],[4]
Equity Securities International Small-cap Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	0	[1],[4]	0	[1],[4]
Asset category [Abstract]
Fair value of plan assets	0	[1],[4]	0	[1],[4]
Equity Securities International Mid-cap Value [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	2,100,000	[1],[5]	1,900,000	[1],[5]
Asset category [Abstract]
Fair value of plan assets	2,100,000	[1],[5]	1,900,000	[1],[5]
Equity Securities International Mid-cap Value [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	2,100,000	[1],[5]	1,900,000	[1],[5]
Asset category [Abstract]
Fair value of plan assets	2,100,000	[1],[5]	1,900,000	[1],[5]
Equity Securities International Mid-cap Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	0	[1],[5]	0	[1],[5]
Asset category [Abstract]
Fair value of plan assets	0	[1],[5]	0	[1],[5]
Equity Securities International Mid-cap Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	0	[1],[5]	0	[1],[5]
Asset category [Abstract]
Fair value of plan assets	0	[1],[5]	0	[1],[5]
Equity Securities International Diversified Value [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	500,000	[1],[6]	500,000	[1],[6]
Asset category [Abstract]
Fair value of plan assets	500,000	[1],[6]	500,000	[1],[6]
Equity Securities International Diversified Value [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	500,000	[1],[6]	500,000	[1],[6]
Asset category [Abstract]
Fair value of plan assets	500,000	[1],[6]	500,000	[1],[6]
Equity Securities International Diversified Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	0	[1],[6]	0	[1],[6]
Asset category [Abstract]
Fair value of plan assets	0	[1],[6]	0	[1],[6]
Equity Securities International Diversified Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Change in fair value of plan assets [Rollforward]
Fair value of plan assets at end of year	0	[1],[6]	0	[1],[6]
Asset category [Abstract]
Fair value of plan assets	$ 0	[1],[6]	$ 0	[1],[6]

[1] See Note 15, Fair Value Measurements, for a description of the three levels within the fair value hierarchy.

[2] Debt securities that specialize in investment grade bonds of institutional investors and other treasury related securities.

[3] Generally, money market securities that maintain cash for interim purchases.

[4] Equity securities that focus on international public companies with low market capitalization.

[5] Equity securities that focus on international public companies with a mid-rated market capitalization.

[6] Equity securities that focus on international public companies but diversify their market capitalization to limit investment.