Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2013

Fair Value Disclosures [Abstract]

Fair value assets and liabilities measured on recurring basis

	Total			Quoted Price in Active Market (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
December 31, 2013:
Cash Equivalents, Marketable Securities and Restricted Investments:
Money market funds	$	72,514		$	72,514	$	—	$	—
Certificates of deposit	1,116			1,116		—		—
Corporate notes	103,946			—		103,946		—
Commercial paper	19,973			—		19,973		—
U.S. government treasury securities	52,390			52,390		—		—
Securities of government-sponsored entities	118,250			—		118,250		—
Total cash equivalents, marketable securities and restricted investments	$	368,189		$	126,020	$	242,169	$	—
Contingent Consideration:
Acquisition-related liabilities, current	$	(616	)	$	—	$	—	$	(616	)
Acquisition-related liabilities, non-current	(596		)	—		—		(596		)
Total contingent consideration	$	(1,212	)	$	—	$	—	$	(1,212	)
December 31, 2012:
Cash Equivalents, Marketable Securities and Restricted Investments:
Money market funds	$	89,101		$	89,101	$	—	$	—
Certificates of deposit	998			998		—		—
Corporate notes	42,447			—		42,447		—
Commercial paper	9,997			—		9,997		—
U.S. government treasury securities	56,472			56,472		—		—
Securities of government-sponsored entities	198,326			—		198,326		—
Total cash equivalents, marketable securities and restricted investments	$	397,341		$	146,571	$	250,770	$	—
Contingent Consideration:
Acquisition-related liabilities, non-current	$	(1,074	)	$	—	$	—	$	(1,074	)

Estimated fair value for the Company's Assets and Liabilities measured using significant unobservable inputs (Level 3)

	December 31,
	2013		2012
Fair value measurement at beginning of period	$	1,074	$	32,221
Contingent consideration liability recorded upon acquisition	—		1,019
Change in fair value measurement included in operating expenses	138		1,364
Contingent consideration paid or settled	—		(33,530		)
Fair value measurement at end of period	$	1,212	$	1,074