Financial Instruments and Fair Value Measurements - Composition of Marketable Securities (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Cost	$ 67,718	$ 278,290
Available-for-sale Securities, Gross Unrealized Gains, Before Tax	37	5
Available-for-sale Securities, Gross Unrealized Losses, Before Tax	(20)	(540)
Available-for-sale Securities, Fair Value	67,735	277,755
Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Cost	54,077	165,629
Available-for-sale Securities, Gross Unrealized Gains, Before Tax	18	5
Available-for-sale Securities, Gross Unrealized Losses, Before Tax	(14)	(211)
Available-for-sale Securities, Fair Value	54,081	165,423
Long-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Cost	13,641	112,661
Available-for-sale Securities, Gross Unrealized Gains, Before Tax	19
Available-for-sale Securities, Gross Unrealized Losses, Before Tax	(6)	(329)
Available-for-sale Securities, Fair Value	13,654	112,332
Commercial paper [Member] | Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Cost	10,453	21,991
Available-for-sale Securities, Fair Value	$ 10,453	$ 21,991
Commercial paper [Member] | Maximum [Member] | Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities Contractual Maturity	1 year	1 year
Certificates of deposit [Member] | Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Cost		$ 6,615
Available-for-sale Securities, Fair Value		6,615
Certificates of deposit [Member] | Long-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Cost		12,392
Available-for-sale Securities, Fair Value		$ 12,392
Certificates of deposit [Member] | Maximum [Member] | Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities Contractual Maturity		1 year
Certificates of deposit [Member] | Maximum [Member] | Long-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities Contractual Maturity		2 years
Certificates of deposit [Member] | Minimum [Member] | Long-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities Contractual Maturity		1 year
Corporate notes [Member] | Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Cost	$ 37,130	$ 108,739
Available-for-sale Securities, Gross Unrealized Gains, Before Tax	9	5
Available-for-sale Securities, Gross Unrealized Losses, Before Tax	(14)	(173)
Available-for-sale Securities, Fair Value	37,125	108,571
Corporate notes [Member] | Long-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Cost	11,044	43,857
Available-for-sale Securities, Gross Unrealized Gains, Before Tax	13
Available-for-sale Securities, Gross Unrealized Losses, Before Tax	(6)	(109)
Available-for-sale Securities, Fair Value	$ 11,051	$ 43,748
Corporate notes [Member] | Maximum [Member] | Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities Contractual Maturity	1 year	1 year
Corporate notes [Member] | Maximum [Member] | Long-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities Contractual Maturity	2 years	2 years
Corporate notes [Member] | Minimum [Member] | Long-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities Contractual Maturity	1 year	1 year
Securities of government-sponsored entities [Member] | Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Cost	$ 6,494	$ 28,284
Available-for-sale Securities, Gross Unrealized Gains, Before Tax	9
Available-for-sale Securities, Gross Unrealized Losses, Before Tax		(38)
Available-for-sale Securities, Fair Value	6,503	28,246
Securities of government-sponsored entities [Member] | Long-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Cost	2,597	56,412
Available-for-sale Securities, Gross Unrealized Gains, Before Tax	6
Available-for-sale Securities, Gross Unrealized Losses, Before Tax		(220)
Available-for-sale Securities, Fair Value	$ 2,603	$ 56,192
Securities of government-sponsored entities [Member] | Maximum [Member] | Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities Contractual Maturity	1 year	1 year
Securities of government-sponsored entities [Member] | Maximum [Member] | Long-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities Contractual Maturity	2 years	2 years
Securities of government-sponsored entities [Member] | Minimum [Member] | Long-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities Contractual Maturity	1 year	1 year