Long-Term Debt (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 29, 2013	Jun. 30, 2012	Jun. 29, 2013	Jun. 30, 2012	Dec. 31, 2012
Debt Instrument [Line Items]
Long-term debt	$ 405,392		$ 405,392		$ 392,931
Less current portion	0		0		0
Long-term debt, less current portion	405,392		405,392		392,931
Debt Instruments [Abstract]
Principal amount of debt	575,000		575,000		575,000
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	575,000		575,000		575,000
Unamortized discount	(365,627)		(365,627)		(367,414)
Embedded derivative	977		977		1,303
Carrying value of liability component	210,350		210,350		208,889
Equity component - net carrying value	230,214		230,214		230,214
Interest expense related to debentures [Abstract]
Contractual coupon interest	3,235	2,682	6,470	5,073
Non-cash amortization of debt discount	901	697	1,787	1,308
Non-cash amortization of deferred financing costs	48	39	95	73
Non-cash change in value of derivative liability	(18)	222	(326)	43
Total interest expense related to the debentures	4,166	3,640	8,026	6,497
Credit Facility [Member]
Debt Instrument [Line Items]
Long-term debt	100,000		100,000		89,000
Exchangeable Unsecured Notes, Due 2102 [Member]
Debt Instrument [Line Items]
Long-term debt	95,042		95,042		95,042
Convertible Senior Debentures, Due 2040 [Member]
Debt Instrument [Line Items]
Long-term debt	100,891		100,891		100,166
Debt Instruments [Abstract]
Convertible senior debentures issuance date			Nov. 09, 2010
Debt maturity date	Nov. 15, 2040		Nov. 15, 2040
Principal amount of debt	275,000		275,000		275,000
Stated rate of interest on debt (in hundredths)	2.25%		2.25%
Effective rate of interest on convertible senior debentures (in hundredths)			8.00%
Debt Instrument Conversion Price Amount			$ 13.88
Debt instrument, conversion trigger	$ 18.04		$ 18.04
Debt instrument, initial conversion shares of common stock (shares per $1000 principal)			72.0331
Convertible senior debentures call date	Nov. 20, 2020		Nov. 20, 2020
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	275,000		275,000		275,000
Unamortized discount	(174,568)		(174,568)		(175,456)
Embedded derivative	459		459		622
Carrying value of liability component	100,891		100,891		100,166
Equity component - net carrying value	110,094		110,094		110,094
Interest expense related to debentures [Abstract]
Contractual coupon interest	1,547	1,547	3,094	3,094
Non-cash amortization of debt discount	448	414	888	821
Non-cash amortization of deferred financing costs	22	22	44	44
Non-cash change in value of derivative liability	(16)	71	(163)	(33)
Total interest expense related to the debentures	2,001	2,054	3,863	3,926
Convertible Senior Debentures, Due 2041 [Member]
Debt Instrument [Line Items]
Long-term debt	51,760		51,760		51,399
Debt Instruments [Abstract]
Convertible senior debentures issuance date			May 13, 2011
Debt maturity date	May 15, 2041		May 15, 2041
Principal amount of debt	150,000		150,000		150,000
Stated rate of interest on debt (in hundredths)	2.25%		2.25%
Effective rate of interest on convertible senior debentures (in hundredths)			8.375%
Debt Instrument Conversion Price Amount			$ 19.02
Debt instrument, conversion trigger	$ 24.73		$ 24.73
Debt instrument, initial conversion shares of common stock (shares per $1000 principal)			52.5659
Convertible senior debentures call date	May 20, 2021		May 20, 2021
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	150,000		150,000		150,000
Unamortized discount	(98,552)		(98,552)		(99,000)
Embedded derivative	312		312		399
Carrying value of liability component	51,760		51,760		51,399
Equity component - net carrying value	62,246		62,246		62,246
Interest expense related to debentures [Abstract]
Contractual coupon interest	844	844	1,688	1,688
Non-cash amortization of debt discount	226	209	448	413
Non-cash amortization of deferred financing costs	12	12	24	24
Non-cash change in value of derivative liability	1	109	(87)	34
Total interest expense related to the debentures	1,083	1,174	2,073	2,159
Convertible Senior Debentures, Due 2042 [Member]
Debt Instrument [Line Items]
Long-term debt	57,699		57,699		57,324
Debt Instruments [Abstract]
Convertible senior debentures issuance date			May 31, 2012
Debt maturity date	Jun. 01, 2042		Jun. 01, 2042
Principal amount of debt	150,000		150,000		150,000
Stated rate of interest on debt (in hundredths)	2.25%		2.25%
Effective rate of interest on convertible senior debentures (in hundredths)			7.50%
Debt Instrument Conversion Price Amount			$ 11.81
Debt instrument, conversion trigger	$ 15.35		$ 15.35
Debt instrument, initial conversion shares of common stock (shares per $1000 principal)			84.6937
Convertible senior debentures call date	Jun. 07, 2022		Jun. 07, 2022
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	150,000		150,000		150,000
Unamortized discount	(92,507)		(92,507)		(92,958)
Embedded derivative	206		206		282
Carrying value of liability component	57,699		57,699		57,324
Equity component - net carrying value	57,874		57,874		57,874
Interest expense related to debentures [Abstract]
Contractual coupon interest	844	291	1,688	291
Non-cash amortization of debt discount	227	74	451	74
Non-cash amortization of deferred financing costs	14	5	27	5
Non-cash change in value of derivative liability	(3)	42	(76)	42
Total interest expense related to the debentures	$ 1,082	$ 412	$ 2,090	$ 412