Long-Term Debt (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Apr. 04, 2015	Mar. 29, 2014	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term debt	$ 470,905		$ 454,922
Exchangeable unsecured notes, due 2102	38,642		38,642
Credit facility	215,000		200,000
Less current portion	0		0
Long-term debt, less current portion	470,905		454,922
Debt Instruments [Abstract]
Principal amount of debt	575,000		575,000
Debt instrument percentage of conversion price (in hundredths)	130.00%
Debt instrument, Percentage of sale price of common stock (in hundredths)	98.00%
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	575,000		575,000
Unamortized discount	(358,789)		(359,825)
Embedded derivative	1,052		1,105
Carrying value of liability component	217,263		216,280
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	1,036	958
Non-cash amortization of deferred financing costs	47	46
Non-cash change in value of derivative liability	(53)	79
Total interest expense related to the debentures	4,265	4,318
Convertible Senior Debentures, Due 2040 [Member]
Debt Instrument [Line Items]
Convertible Debt, Noncurrent	104,297		103,841
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	$ 17.68
Debt conversion rate	73.5289
Debt effective conversion price	$ 13.60
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	(171,170)		(171,685)
Embedded derivative	467		526
Carrying value of liability component	104,297		103,841
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	515	476
Non-cash amortization of deferred financing costs	22	22
Non-cash change in value of derivative liability	(59)	45
Total interest expense related to the debentures	2,025	2,090
Convertible Senior Debentures, Due 2041 [Member]
Debt Instrument [Line Items]
Convertible Debt, Noncurrent	53,523		53,249
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	$ 24.23
Debt conversion rate	53.6575
Debt effective conversion price	$ 18.64
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	(96,831)		(97,092)
Embedded derivative	354		341
Carrying value of liability component	53,523		53,249
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	261	241
Non-cash amortization of deferred financing costs	12	11
Non-cash change in value of derivative liability	13	14
Total interest expense related to the debentures	1,130	1,110
Convertible Senior Debentures, Due 2042 [Member]
Debt Instrument [Line Items]
Convertible Debt, Noncurrent	59,443		59,190
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	$ 15.04
Debt conversion rate	86.4524
Debt effective conversion price	$ 11.57
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	(90,788)		(91,048)
Embedded derivative	231		238
Carrying value of liability component	59,443		59,190
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	260	241
Non-cash amortization of deferred financing costs	13	13
Non-cash change in value of derivative liability	(7)	20
Total interest expense related to the debentures	$ 1,110	$ 1,118