Long-Term Debt (Details) (USD $)	6 Months Ended				3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended			3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jul. 02, 2011	Mar. 31, 2012	Dec. 31, 2011	Jun. 30, 2012 Convertible Senior Debentures 2040 [Member]	Jul. 02, 2011 Convertible Senior Debentures 2040 [Member]	Jun. 30, 2012 Convertible Senior Debentures 2040 [Member]	Jul. 02, 2011 Convertible Senior Debentures 2040 [Member]	Dec. 31, 2011 Convertible Senior Debentures 2040 [Member]	Jun. 30, 2012 Convertible Senior Debentures 2041 [Member]	Jul. 02, 2011 Convertible Senior Debentures 2041 [Member]	Jun. 30, 2012 Convertible Senior Debentures 2041 [Member]	Jul. 02, 2011 Convertible Senior Debentures 2041 [Member]	Dec. 31, 2011 Convertible Senior Debentures 2041 [Member]	Jun. 30, 2012 Convertible Senior Debentures 2042 [Member]	Jun. 30, 2012 Convertible Senior Debentures 2042 [Member]
Long-Term Debt [Abstract]
Credit facility	$ 160,000,000			$ 155,000,000
Exchangeable unsecured notes, due 2102	95,042,000			95,042,000
Convertible senior debentures					99,251,000		99,251,000		98,463,000	50,996,000		50,996,000		50,549,000	56,884,000	56,884,000
Long-term Debt	462,173,000			399,054,000
Less current portion	0			0
Long-term debt, less current portion	462,173,000			399,054,000
Debt Instrument [Line Items]
Convertible senior debentures issuance date							Nov. 09, 2010					May 13, 2011				May 31, 2012
Principal amount of convertible senior debentures					275,000,000		275,000,000		275,000,000	150,000,000		150,000,000		150,000,000	150,000,000	150,000,000
Common stock, shares repurchased (in shares)	13,948,687															13,948,687
Treasury stock, value, acquired, cost method																150,000,000
Principal amount of the debentures					275,000,000		275,000,000		275,000,000	150,000,000		150,000,000		150,000,000	150,000,000	150,000,000
Unamortized discount					(176,310,000)		(176,310,000)		(177,131,000)	(99,430,000)		(99,430,000)		(99,843,000)	(93,394,000)	(93,394,000)
Embedded derivative					561,000		561,000		594,000	426,000		426,000		392,000	278,000	278,000
Carrying value of liability component					99,251,000		99,251,000		98,463,000	50,996,000		50,996,000		50,549,000	56,884,000	56,884,000
Equity component - net carrying value					110,094,000		110,094,000		110,094,000	62,246,000		62,246,000		62,246,000	57,874,000	57,874,000
Stated rate of interest on convertible senior debentures (in hundredths)					2.25%		2.25%			2.25%		2.25%			2.25%	2.25%
Effective rate of interest on convertible senior debentures (in hundredths)							8.00%					8.375%				7.50%
Contractual coupon interest					1,547,000	1,547,000	3,094,000	3,094,000		844,000	441,000	1,688,000	441,000		291,000	291,000
Non-cash amortization of debt discount	1,308,000	861,000			414,000	383,000	821,000	759,000		209,000	102,000	413,000	102,000		74,000	74,000
Non-cash amortization of deferred financing costs					22,000	22,000	44,000	44,000		12,000	6,000	24,000	6,000		5,000	5,000
Non-cash change in value of derivative liability					71,000	69,000	(33,000)	8,000		109,000	2,000	34,000	2,000		42,000	42,000
Total interest expense related to the debentures					2,054,000	2,021,000	3,926,000	3,905,000		1,174,000	551,000	2,159,000	551,000		412,000	412,000
Debt instrument percentage of conversion price (in hundredths)															130.00%	130.00%
Debt instrument, conversion price amount																15.35
Debt instrument, Percentage of sale price of common stock (in hundredths)															98.00%	98.00%
Debt instrument, initial conversion shares of common stock															84.6937	84.6937
Debt instrument, principal amount of debentures															1,000	1,000
Debt instrument, initial conversion price (in dollars per share)															$ 11.81	$ 11.81
Debt instrument, percentage of initial conversion price premium (in hundredths)															13.75%	13.75%
Debt instrument, conversion price (in dollars per share)															$ 10.38	$ 10.38
Line of Credit Facility, Maximum Borrowing Capacity	528,000,000		450,000,000
Line of Credit Facility, Amendment Fee Amount	$ 390,000