Long-Term Debt (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 29, 2014	Mar. 30, 2013	Dec. 31, 2013
Debt Instrument [Line Items]
Long-term debt	$ 361,948		$ 364,911
Exchangeable unsecured notes, due 2102	38,642		38,642
Credit facility	110,000		114,000
Less current portion	0		0
Long-term debt, less current portion	361,948		364,911
Debt Instruments [Abstract]
Principal amount of debt	575,000		575,000
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	575,000		575,000
Unamortized discount	(362,810)		(363,768)
Embedded derivative	1,116		1,037
Carrying value of liability component	213,306		212,269
Equity component - net carrying value	230,214		230,214
Interest expense related to debentures [Abstract]
Contractual coupon interest	3,235	3,235
Non-cash amortization of debt discount	958	886
Non-cash amortization of deferred financing costs	46	47
Non-cash change in value of derivative liability	79	(308)
Total interest expense related to the debentures	4,318	3,860
Convertible Senior Debentures 2040 [Member]
Debt Instrument [Line Items]
Convertible Debt, Noncurrent	102,367		101,846
Debt Instruments [Abstract]
Issuance date	Nov. 09, 2010
Debt maturity date	Nov. 15, 2040
Principal amount of debt	275,000		275,000
Stated rate of interest on debt (in hundredths)	2.25%
Effective rate of interest on convertible senior debentures (in hundredths)	8.00%
Debt Instrument, Convertible, Stock Price Trigger	$ 17.97
Debt conversion rate	72.3396
Debt effective conversion price	$ 13.82
Convertible senior debentures call date	Nov. 20, 2020
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	275,000		275,000
Unamortized discount	(173,169)		(173,645)
Embedded derivative	536		491
Carrying value of liability component	102,367		101,846
Equity component - net carrying value	110,094		110,094
Interest expense related to debentures [Abstract]
Contractual coupon interest	1,547	1,547
Non-cash amortization of debt discount	476	440
Non-cash amortization of deferred financing costs	22	22
Non-cash change in value of derivative liability	45	(147)
Total interest expense related to the debentures	2,090	1,862
Convertible Senior Debentures 2041 [Member]
Debt Instrument [Line Items]
Convertible Debt, Noncurrent	52,519		52,264
Debt Instruments [Abstract]
Issuance date	May 13, 2011
Debt maturity date	May 15, 2041
Principal amount of debt	150,000		150,000
Stated rate of interest on debt (in hundredths)	2.25%
Effective rate of interest on convertible senior debentures (in hundredths)	8.375%
Debt Instrument, Convertible, Stock Price Trigger	$ 24.62
Debt conversion rate	52.7896
Debt effective conversion price	$ 18.94
Convertible senior debentures call date	May 20, 2021
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	150,000		150,000
Unamortized discount	(97,844)		(98,085)
Embedded derivative	363		349
Carrying value of liability component	52,519		52,264
Equity component - net carrying value	62,246		62,246
Interest expense related to debentures [Abstract]
Contractual coupon interest	844	844
Non-cash amortization of debt discount	241	222
Non-cash amortization of deferred financing costs	11	12
Non-cash change in value of derivative liability	14	(88)
Total interest expense related to the debentures	1,110	990
Convertible Senior Debentures 2042 [Member]
Debt Instrument [Line Items]
Convertible Debt, Noncurrent	58,420		58,159
Debt Instruments [Abstract]
Issuance date	May 31, 2012
Debt maturity date	Jun. 01, 2042
Principal amount of debt	150,000		150,000
Stated rate of interest on debt (in hundredths)	2.25%
Effective rate of interest on convertible senior debentures (in hundredths)	7.50%
Debt Instrument, Convertible, Stock Price Trigger	$ 15.29
Debt conversion rate	85.0541
Debt effective conversion price	$ 11.76
Convertible senior debentures call date	Jun. 07, 2022
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	150,000		150,000
Unamortized discount	(91,797)		(92,038)
Embedded derivative	217		197
Carrying value of liability component	58,420		58,159
Equity component - net carrying value	57,874		57,874
Interest expense related to debentures [Abstract]
Contractual coupon interest	844	844
Non-cash amortization of debt discount	241	224
Non-cash amortization of deferred financing costs	13	13
Non-cash change in value of derivative liability	20	(73)
Total interest expense related to the debentures	$ 1,118	$ 1,008