Fair Value Measurements (Details) (USD $)					3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Convertible senior notes due 2016	Aug. 31, 2009 Convertible senior notes due 2016	Mar. 31, 2013 Auction rate securities	Mar. 31, 2013 Auction rate securities Maximum	Mar. 31, 2013 Fair Value, Measurements, Recurring As reflected on the balance sheet	Dec. 31, 2012 Fair Value, Measurements, Recurring As reflected on the balance sheet	Mar. 31, 2013 Fair Value, Measurements, Recurring As reflected on the balance sheet Money market funds	Dec. 31, 2012 Fair Value, Measurements, Recurring As reflected on the balance sheet Money market funds	Mar. 31, 2013 Fair Value, Measurements, Recurring As reflected on the balance sheet Corporate and financial institutions debt	Dec. 31, 2012 Fair Value, Measurements, Recurring As reflected on the balance sheet Corporate and financial institutions debt	Mar. 31, 2013 Fair Value, Measurements, Recurring As reflected on the balance sheet Auction rate securities	Dec. 31, 2012 Fair Value, Measurements, Recurring As reflected on the balance sheet Auction rate securities	Mar. 31, 2013 Fair Value, Measurements, Recurring As reflected on the balance sheet U.S. government agencies	Dec. 31, 2012 Fair Value, Measurements, Recurring As reflected on the balance sheet U.S. government agencies	Mar. 31, 2013 Fair Value, Measurements, Recurring As reflected on the balance sheet U.S. treasury bills	Dec. 31, 2012 Fair Value, Measurements, Recurring As reflected on the balance sheet U.S. treasury bills	Mar. 31, 2013 Fair Value, Measurements, Recurring Level 1	Dec. 31, 2012 Fair Value, Measurements, Recurring Level 1	Mar. 31, 2013 Fair Value, Measurements, Recurring Level 1 Money market funds	Dec. 31, 2012 Fair Value, Measurements, Recurring Level 1 Money market funds	Mar. 31, 2013 Fair Value, Measurements, Recurring Level 1 U.S. treasury bills	Dec. 31, 2012 Fair Value, Measurements, Recurring Level 1 U.S. treasury bills	Mar. 31, 2013 Fair Value, Measurements, Recurring Level 2	Dec. 31, 2012 Fair Value, Measurements, Recurring Level 2	Mar. 31, 2013 Fair Value, Measurements, Recurring Level 2 Corporate and financial institutions debt	Dec. 31, 2012 Fair Value, Measurements, Recurring Level 2 Corporate and financial institutions debt	Mar. 31, 2013 Fair Value, Measurements, Recurring Level 2 U.S. government agencies	Dec. 31, 2012 Fair Value, Measurements, Recurring Level 2 U.S. government agencies	Mar. 31, 2013 Fair Value, Measurements, Recurring Level 3	Dec. 31, 2012 Fair Value, Measurements, Recurring Level 3	Mar. 31, 2013 Fair Value, Measurements, Recurring Level 3 Auction rate securities	Dec. 31, 2012 Fair Value, Measurements, Recurring Level 3 Auction rate securities	Mar. 31, 2013 Fair Value, Measurements, Recurring Total fair value	Dec. 31, 2012 Fair Value, Measurements, Recurring Total fair value	Mar. 31, 2013 Fair Value, Measurements, Recurring Total fair value Money market funds	Dec. 31, 2012 Fair Value, Measurements, Recurring Total fair value Money market funds	Mar. 31, 2013 Fair Value, Measurements, Recurring Total fair value Corporate and financial institutions debt	Dec. 31, 2012 Fair Value, Measurements, Recurring Total fair value Corporate and financial institutions debt	Mar. 31, 2013 Fair Value, Measurements, Recurring Total fair value Auction rate securities	Dec. 31, 2012 Fair Value, Measurements, Recurring Total fair value Auction rate securities	Mar. 31, 2013 Fair Value, Measurements, Recurring Total fair value U.S. government agencies	Dec. 31, 2012 Fair Value, Measurements, Recurring Total fair value U.S. government agencies	Mar. 31, 2013 Fair Value, Measurements, Recurring Total fair value U.S. treasury bills	Dec. 31, 2012 Fair Value, Measurements, Recurring Total fair value U.S. treasury bills
Assets:
Total							$ 374,215,000	$ 374,409,000	$ 11,496,000	$ 19,297,000	$ 249,127,000	$ 229,053,000	$ 8,178,000	$ 8,323,000	$ 71,100,000	$ 88,514,000	$ 34,314,000	$ 29,222,000	$ 45,810,000	$ 48,519,000	$ 11,496,000	$ 19,297,000	$ 34,314,000	$ 29,222,000	$ 320,227,000	$ 317,567,000	$ 249,127,000	$ 229,053,000	$ 71,100,000	$ 88,514,000	$ 8,178,000	$ 8,323,000	$ 8,178,000	$ 8,323,000	$ 374,215,000	$ 374,409,000	$ 11,496,000	$ 19,297,000	$ 249,127,000	$ 229,053,000	$ 8,178,000	$ 8,323,000	$ 71,100,000	$ 88,514,000	$ 34,314,000	$ 29,222,000
Liabilities:
Liability for contingent consideration, current and non-current							152,093,000	149,163,000																							152,093,000	149,163,000			152,093,000	149,163,000
Convertible senior notes due 2016 (face value $230,000)							177,503,000	174,404,000																	537,038,000	468,533,000									537,038,000	468,533,000
Total							329,596,000	323,567,000																	537,038,000	468,533,000					152,093,000	149,163,000			689,131,000	617,696,000
Face value			230,000,000	230,000,000
Discount rates used in the cash flow analysis (as a percent)					1.87%
Change in the auction rate securities valuation as a result of a 1% increase or decrease in the discount rate					400,000
Percent change to evaluate change in the auction rate securities valuation					1.00%
Expected holding period					5 years
Change in holding period used to evaluate the effect on auction rate securities valuation					1 year
Change in auction rate securities valuation by 1 year increase or decrease in holding period						100,000
Transfers from level 1 to level 2 assets	0	0
Transfers from level 2 to level 1 assets	$ 0	$ 0