Long-Term Debt (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 30, 2013	Mar. 31, 2012	Dec. 31, 2012
Debt Instrument [Line Items]
Long-term debt	$ 394,509		$ 392,931
Less current portion	0		0
Long-term debt, less current portion	394,509		392,931
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	(366,528)		(367,414)
Embedded derivative	995		1,303
Carrying value of liability component	209,467		208,889
Equity component - net carrying value	230,214		230,214
Interest expense related to debentures [Abstract]
Contractual coupon interest	3,235	2,391
Non-cash amortization of debt discount	886	611
Non-cash amortization of deferred financing costs	47	34
Non-cash change in value of derivative liability	(308)	(179)
Total interest expense related to the debentures	3,860	2,857
Credit Facility [Member]
Debt Instrument [Line Items]
Long-term debt	90,000		89,000
Exchangeable Unsecured Notes, Due 2102 [Member]
Debt Instrument [Line Items]
Long-term debt	95,042		95,042
Convertible Senior Debentures, Due 2040 [Member]
Debt Instrument [Line Items]
Long-term debt	100,459		100,166
Debt Instruments [Abstract]
Convertible senior debentures 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 Conversion Price Amount	$ 13.88
Debt instrument, conversion trigger	$ 18.04
Debt instrument, initial conversion shares of common stock (shares per $1000 principal)	72.0331
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	(175,016)		(175,456)
Embedded derivative	475		622
Carrying value of liability component	100,459		100,166
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	440	407
Non-cash amortization of deferred financing costs	22	22
Non-cash change in value of derivative liability	(147)	(104)
Total interest expense related to the debentures	1,862	1,872
Convertible Senior Debentures, Due 2041 [Member]
Debt Instrument [Line Items]
Long-term debt	51,533		51,399
Debt Instruments [Abstract]
Convertible senior debentures 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 Conversion Price Amount	$ 19.02
Debt instrument, conversion trigger	$ 24.73
Debt instrument, initial conversion shares of common stock (shares per $1000 principal)	52.5659
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	(98,778)		(99,000)
Embedded derivative	311		399
Carrying value of liability component	51,533		51,399
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	222	204
Non-cash amortization of deferred financing costs	12	12
Non-cash change in value of derivative liability	(88)	(75)
Total interest expense related to the debentures	990	985
Convertible Senior Debentures 2042 [Member]
Debt Instrument [Line Items]
Long-term debt	57,475		57,324
Debt Instruments [Abstract]
Convertible senior debentures 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 Conversion Price Amount	$ 11.81
Debt instrument, conversion trigger	$ 15.35
Debt instrument, initial conversion shares of common stock (shares per $1000 principal)	84.6937
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	(92,734)		(92,958)
Embedded derivative	209		282
Carrying value of liability component	57,475		57,324
Equity component - net carrying value	57,874		57,874
Interest expense related to debentures [Abstract]
Contractual coupon interest	844
Non-cash amortization of debt discount	224
Non-cash amortization of deferred financing costs	13
Non-cash change in value of derivative liability	(73)
Total interest expense related to the debentures	$ 1,008