Financial Instruments and Fair Value Measurements - Composition of Marketable Securities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Cost	$ 60,849	$ 278,290
Available-for-sale Securities, Gross Unrealized Gains, Before Tax	33	5
Available-for-sale Securities, Gross Unrealized Losses, Before Tax	(6)	(540)
Available-for-sale Securities, Fair Value	60,876	277,755
Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Cost	42,487	165,629
Available-for-sale Securities, Gross Unrealized Gains, Before Tax	12	5
Available-for-sale Securities, Gross Unrealized Losses, Before Tax	(4)	(211)
Available-for-sale Securities, Fair Value	42,495	165,423
Long-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Cost	18,362	112,661
Available-for-sale Securities, Gross Unrealized Gains, Before Tax	21
Available-for-sale Securities, Gross Unrealized Losses, Before Tax	(2)	(329)
Available-for-sale Securities, Fair Value	18,381	112,332
Commercial paper [Member] | Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Cost	23,865	21,991
Available-for-sale Securities, Fair Value	$ 23,865	$ 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	$ 18,622	$ 108,739
Available-for-sale Securities, Gross Unrealized Gains, Before Tax	12	5
Available-for-sale Securities, Gross Unrealized Losses, Before Tax	(4)	(173)
Available-for-sale Securities, Fair Value	18,630	108,571
Corporate notes [Member] | Long-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-sale Securities, Cost	7,772	43,857
Available-for-sale Securities, Gross Unrealized Gains, Before Tax	10
Available-for-sale Securities, Gross Unrealized Losses, Before Tax	(2)	(109)
Available-for-sale Securities, Fair Value	$ 7,780	$ 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		$ 28,284
Available-for-sale Securities, Gross Unrealized Losses, Before Tax		(38)
Available-for-sale Securities, Fair Value		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	$ 10,590	56,412
Available-for-sale Securities, Gross Unrealized Gains, Before Tax	11
Available-for-sale Securities, Gross Unrealized Losses, Before Tax		(220)
Available-for-sale Securities, Fair Value	$ 10,601	$ 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
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