Employee benefit plans (Details) (USD $)	12 Months Ended
	Dec. 30, 2011		Dec. 31, 2010		Dec. 25, 2009
Employee benefit plans [Abstract]
Net periodic benefit income (expense)	$ (800,000)		$ 1,100,000		$ 9,500,000
Securities designated for funding benefit payments					7,400,000
Defined Benefit Plan Disclosure [Line Items]
Expected contributions to defined benefit plans in next fiscal year	100,000
Approximate accelerated funding that may be required for defined benefit plan	7,300,000
Securities distributed to settle obligations of defined benefit supplemental retirement plan			13,600,000
Accumulated other comprehensive income [Abstract]
Pension cost expected to be amortized from accumulated other comprehensive income	0
Expected benefit payments [Abstract]
Defined contribution pension plan expense of non-U.S. subsidiaries	1,200,000		2,600,000		2,800,000
Contribution expense under 401(k) plans	1,000,000		300,000		300,000
Pension Plans [Member]
Net pension cost related to defined benefit plans [Abstract]
Service cost	38,000		296,000		1,120,000
Interest cost	1,811,000		1,860,000		2,327,000
Expected return on plan assets	(2,496,000)		(2,290,000)		(1,948,000)
Amortization of transition obligation	5,000		5,000		5,000
Amortization of prior service costs	3,000		17,000		120,000
Recognized actuarial losses (gains)	(26,000)		0		52,000
Curtailment gains	(152,000)		(1,031,000)		(949,000)
Special termination benefits	0		2,225,000		8,820,000
Net periodic pension cost	(817,000)		1,082,000		9,547,000
Change in benefit obligation [Abstract]
Projected benefit obligation at beginning of year	34,628,000		45,201,000
Service cost	38,000		296,000		1,120,000
Interest cost	1,811,000		1,860,000		2,327,000
Actuarial losses	3,699,000		2,048,000
Benefits paid	(1,934,000)		(2,265,000)
Plan amendments/settlements	0		(13,631,000)
Plan curtailments	(47,000)		(1,106,000)
Special termination benefits	0		2,225,000
Projected benefit obligation at end of year	38,195,000		34,628,000		45,201,000
Change in fair value of plan assets [Abstract]
Fair value of plan assets at beginning of year	32,459,000		29,749,000
Actual return on plan assets	2,880,000		4,591,000
Employer contributions	164,000		14,015,000
Benefits paid	(1,934,000)		(2,265,000)
Plan settlements	0		(13,631,000)
Fair value of plan assets at end of year	33,569,000		32,459,000		29,749,000
Accumulated benefit obligation	37,506,000		34,277,000
Accumulated other comprehensive income [Abstract]
Actuarial gains	(3,096,000)		273,000
Plan curtailment	(84,000)		0
Amortization of prior service costs	(21,000)		(7,000)
Amortization of transition obligations	(10,000)		(14,000)
Accumulated other comprehensive income	(3,211,000)		252,000
Benefit obligations in excess of plan assets [Abstract]
Benefit obligation	37,833,000		34,190,000
Accumulated benefit obligation	37,725,000		34,017,000
Plan assets	33,026,000		31,979,000
Asset category [Abstract]
Equity securities (in hundredths)	10.00%		69.00%
Fixed income securities (in hundredths)	88.00%		30.00%
Other (in hundredths)	2.00%		1.00%
Total (in hundredths)	100.00%		100.00%
Fair value of plan assets	33,600,000	[1]	32,500,000	[1]
Assumptions used to develop defined benefit plan [Abstract]
Discount rate (in hundredths)	4.60%		5.40%
Annual compensation increases (in hundredths)			4.25%
Expected long-term rates of return on plan assets (in hundredths)	8.00%		8.00%
Expected benefit payments [Abstract]
2012	1,975,000
2013	2,022,000
2014	2,029,000
2015	2,077,000
2016	2,160,000
Thereafter	27,932,000
Amounts recognized on the Consolidated Balance Sheets
Non-current assets	181,000		101,000
Non-current liabilities	(4,807,000)		(2,270,000)
Net amount recorded	(4,626,000)		(2,169,000)
Quoted Prices In Active markets for Identical Assets (Level 1) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	33,600,000	[1]	32,500,000	[1]
Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets			0	[1],[2]
Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	0	[1]	0	[1]
Cash and Cash Equivalents [Member] | Pension Plans [Member]
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]
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]
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]
Asset category [Abstract]
Fair value of plan assets	0	[1]	0	[1]
Fixed Income Securities US Treasuries [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets			2,400,000	[1],[3]
Fixed Income Securities US Treasuries [Member] | Quoted Prices In Active markets for Identical Assets (Level 1) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets			2,400,000	[1],[3]
Fixed Income Securities US Treasuries [Member] | Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	0	[1],[3]
Fixed Income Securities US Treasuries [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets			0	[1],[3]
Fixed Income Securities Corporate Bonds [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	29,100,000	[1],[4]	7,100,000	[1],[4]
Fixed Income Securities Corporate Bonds [Member] | Quoted Prices In Active markets for Identical Assets (Level 1) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	29,100,000	[1],[4]	7,100,000	[1],[4]
Fixed Income Securities Corporate Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	0	[1],[4]	0	[1],[4]
Fixed Income Securities Corporate Bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	0	[1],[4]	0	[1],[4]
Fixed Income Securities Short-term Debt Securities [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	1,000,000	[1],[5]	1,000,000	[1],[5]
Fixed Income Securities Short-term Debt Securities [Member] | Quoted Prices In Active markets for Identical Assets (Level 1) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	1,000,000	[1],[5]	1,000,000	[1],[5]
Fixed Income Securities Short-term Debt Securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	0	[1],[5]	0	[1],[5]
Fixed Income Securities Short-term Debt Securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	0	[1],[5]	0	[1],[5]
Equity Securities International Small-cap Value [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	1,000,000	[1],[6]	6,200,000	[1],[6]
Equity Securities International Small-cap Value [Member] | Quoted Prices In Active markets for Identical Assets (Level 1) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	1,000,000	[1],[6]	6,200,000	[1],[6]
Equity Securities International Small-cap Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	0	[1],[6]	0	[1],[6]
Equity Securities International Small-cap Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	0	[1],[6]	0	[1],[6]
Equity Securities International Mid-cap Value [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	1,900,000	[1],[7]	12,500,000	[1],[7]
Equity Securities International Mid-cap Value [Member] | Quoted Prices In Active markets for Identical Assets (Level 1) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	1,900,000	[1],[7]	12,500,000	[1],[7]
Equity Securities International Mid-cap Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	0	[1],[7]	0	[1],[7]
Equity Securities International Mid-cap Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	0	[1],[7]	0	[1],[7]
Equity Securities International Diversified Value [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	500,000	[1],[2]	3,200,000	[1],[2]
Equity Securities International Diversified Value [Member] | Quoted Prices In Active markets for Identical Assets (Level 1) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	500,000	[1],[2]	3,200,000	[1],[2]
Equity Securities International Diversified Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets			0	[1],[2]
Equity Securities International Diversified Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Asset category [Abstract]
Fair value of plan assets	$ 0	[1],[2]	$ 0	[1],[2]

[1] See Note 15, Financial instruments, for a description of the three levels within the fair value hierarchy.

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

[3] Debt securities that invest in treasury and other related instruments.

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

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

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

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