Financial Instruments and Fair Value Measurements - Fair Value of Assets and Liabilities (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Fair Value Disclosure	$ 455,900,000		$ 455,900,000		$ 439,300,000
Goodwill and Intangible Asset Impairment	0	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	387,192,000		387,192,000		368,189,000
Contingent Consideration Fair Value Disclosure, Current	(612,000)		(612,000)		(616,000)
Acquisition-related liabilities, non-current					(596,000)
Contingent Consideration:
Acquisition-related liabilities	(612,000)		(612,000)		(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	41,025,000		41,025,000		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	572,000		572,000		1,116,000
Fair value measurements on recurring basis [Member] | Corporate notes [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	144,633,000		144,633,000		103,946,000
Fair value measurements on recurring basis [Member] | Commercial paper [Member]
Marketable Securities and Restricted Investments
Total marketable securities and restricted investments	2,497,000		2,497,000		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	59,472,000		59,472,000		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	138,993,000		138,993,000		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	101,069,000		101,069,000		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	41,025,000		41,025,000		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	572,000		572,000		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	59,472,000		59,472,000		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	286,123,000		286,123,000		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	144,633,000		144,633,000		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	2,497,000		2,497,000		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	138,993,000		138,993,000		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	(612,000)		(612,000)		(616,000)
Acquisition-related liabilities, non-current					(596,000)
Contingent Consideration:
Acquisition-related liabilities	(612,000)		(612,000)		(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