Investments - Schedule of Marketable Securities with Unrealized Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Fair Value
Less Than 12 months	$ 104,974	$ 203,065
More than 12 months	8,094	14,834
Total	113,068	217,899
Unrealized Loss
Less Than 12 months	(167)	(565)
More than 12 months	(4)	(10)
Total	(171)	(575)
Asset-backed securities
Fair Value
Less Than 12 months	45,486	57,866
More than 12 months	250	5,923
Total	45,736	63,789
Unrealized Loss
Less Than 12 months	(80)	(192)
More than 12 months	0	(3)
Total	(80)	(195)
Corporate debt securities
Fair Value
Less Than 12 months	55,487	101,701
More than 12 months	7,844	8,911
Total	63,331	110,612
Unrealized Loss
Less Than 12 months	(85)	(289)
More than 12 months	(4)	(7)
Total	(89)	(296)
Commercial paper
Fair Value
Less Than 12 months		11,374
More than 12 months		0
Total		11,374
Unrealized Loss
Less Than 12 months		(9)
More than 12 months		0
Total		(9)
Government agency securities
Fair Value
Less Than 12 months	2,002	24,628
More than 12 months	0	0
Total	2,002	24,628
Unrealized Loss
Less Than 12 months	0	(72)
More than 12 months	0	0
Total	0	(72)
Other securities
Fair Value
Less Than 12 months	1,999	7,496
More than 12 months	0	0
Total	1,999	7,496
Unrealized Loss
Less Than 12 months	(2)	(3)
More than 12 months	0	0
Total	$ (2)	$ (3)