Financial Instruments and Fair Value Measurements - Fair Value of Assets and Liabilities (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Fair Value Disclosure	$ 458,900,000		$ 458,900,000		$ 439,300,000
Goodwill and Intangible Asset Impairment	10,708,000	0	10,708,000	0
Contingent Consideration:
Asset Impairment Charges			2,200,000
Fair value measurements on recurring basis [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	377,208,000		377,208,000		368,189,000
Contingent Consideration Fair Value Disclosure, Current	(648,000)		(648,000)		(616,000)
Acquisition-related liabilities, non-current					(596,000)
Contingent Consideration:
Acquisition-related liabilities	(648,000)		(648,000)		(1,212,000)
Fair value measurements on recurring basis [Member] | Money Market Funds [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	55,092,000		55,092,000		72,514,000
Fair value measurements on recurring basis [Member] | Certificates of deposit [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	869,000		869,000		1,116,000
Fair value measurements on recurring basis [Member] | Corporate notes [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	137,075,000		137,075,000		103,946,000
Fair value measurements on recurring basis [Member] | Commercial paper [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	10,000,000		10,000,000		19,973,000
Fair value measurements on recurring basis [Member] | U.S. government treasury securities [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	49,366,000		49,366,000		52,390,000
Fair value measurements on recurring basis [Member] | Securities of government-sponsored entities [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	124,806,000		124,806,000		118,250,000
Fair value measurements on recurring basis [Member] | Quoted price in active market (Level 1) [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	105,327,000		105,327,000		126,020,000
Contingent Consideration Fair Value Disclosure, Current	0		0		0
Acquisition-related liabilities, non-current					0
Contingent Consideration:
Acquisition-related liabilities	0		0		0
Fair value measurements on recurring basis [Member] | Quoted price in active market (Level 1) [Member] | Money Market Funds [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	55,092,000		55,092,000		72,514,000
Fair value measurements on recurring basis [Member] | Quoted price in active market (Level 1) [Member] | Certificates of deposit [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	869,000		869,000		1,116,000
Fair value measurements on recurring basis [Member] | Quoted price in active market (Level 1) [Member] | Corporate notes [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	0		0		0
Fair value measurements on recurring basis [Member] | Quoted price in active market (Level 1) [Member] | Commercial paper [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	0		0		0
Fair value measurements on recurring basis [Member] | Quoted price in active market (Level 1) [Member] | U.S. government treasury securities [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	49,366,000		49,366,000		52,390,000
Fair value measurements on recurring basis [Member] | Quoted price in active market (Level 1) [Member] | Securities of government-sponsored entities [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	0		0		0
Fair value measurements on recurring basis [Member] | Significant other observable inputs (Level 2) [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	271,881,000		271,881,000		242,169,000
Contingent Consideration Fair Value Disclosure, Current	0		0		0
Acquisition-related liabilities, non-current					0
Contingent Consideration:
Acquisition-related liabilities	0		0		0
Fair value measurements on recurring basis [Member] | Significant other observable inputs (Level 2) [Member] | Money Market Funds [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	0		0		0
Fair value measurements on recurring basis [Member] | Significant other observable inputs (Level 2) [Member] | Certificates of deposit [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	0		0		0
Fair value measurements on recurring basis [Member] | Significant other observable inputs (Level 2) [Member] | Corporate notes [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	137,075,000		137,075,000		103,946,000
Fair value measurements on recurring basis [Member] | Significant other observable inputs (Level 2) [Member] | Commercial paper [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	10,000,000		10,000,000		19,973,000
Fair value measurements on recurring basis [Member] | Significant other observable inputs (Level 2) [Member] | U.S. government treasury securities [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	0		0		0
Fair value measurements on recurring basis [Member] | Significant other observable inputs (Level 2) [Member] | Securities of government-sponsored entities [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	124,806,000		124,806,000		118,250,000
Fair value measurements on recurring basis [Member] | Significant unobservable inputs (Level 3) [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	0		0		0
Contingent Consideration Fair Value Disclosure, Current	(648,000)		(648,000)		(616,000)
Acquisition-related liabilities, non-current					(596,000)
Contingent Consideration:
Acquisition-related liabilities	(648,000)		(648,000)		(1,212,000)
Fair value measurements on recurring basis [Member] | Significant unobservable inputs (Level 3) [Member] | Money Market Funds [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	0		0		0
Fair value measurements on recurring basis [Member] | Significant unobservable inputs (Level 3) [Member] | Certificates of deposit [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	0		0		0
Fair value measurements on recurring basis [Member] | Significant unobservable inputs (Level 3) [Member] | Corporate notes [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	0		0		0
Fair value measurements on recurring basis [Member] | Significant unobservable inputs (Level 3) [Member] | Commercial paper [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	0		0		0
Fair value measurements on recurring basis [Member] | Significant unobservable inputs (Level 3) [Member] | U.S. government treasury securities [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	0		0		0
Fair value measurements on recurring basis [Member] | Significant unobservable inputs (Level 3) [Member] | Securities of government-sponsored entities [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	$ 0		$ 0		$ 0