Convertible Senior Notes (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011 number	Jun. 30, 2010	Jun. 30, 2011 number	Jun. 30, 2010	Dec. 31, 2010
Convertible Senior Notes [Abstract]
Notes Principal Amount	$ 230,000,000		$ 230,000,000
Interest per annum on Senior Notes	2.25%		2.25%
Stock Conversion shares			25.6419
Principle amount per Note	1,000		1,000
Initial Conversion Price	$ 39.00		$ 39.00
Expected life of the Notes in years	5		5
Remaining amortization period of discount (in months)	3		3
Liability Component Principal Amount	134,293,000		134,293,000
Liability Component Net Carrying Amount	132,272,000		132,272,000		128,261,000
Liability Component Unamortized Discount	2,021,000		2,021,000
Equity Component Carrying Amount	35,515,000		35,515,000
Effective interest rate of Notes			8.50%
Notes Contractual Interest Exp	754,000	792,000	1,510,000	1,552,000
Amortization of Debt Discount	2,027,000	1,873,000	4,011,000	3,707,000
Amortization of Debt issuance cost	138,000	136,000	275,000	274,000
Total	$ 2,919,000	$ 2,801,000	$ 5,796,000	$ 5,533,000