Cash, Cash Equivalents and Marketable Securities - Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 50,058	$ 62,908
Gross Unrealized Gains	2	1
Gross Unrealized Losses	(96)	(59)
Fair Value	49,964	62,850
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	35,869	61,108
Gross Unrealized Gains	2	1
Gross Unrealized Losses	(72)	(59)
Fair Value	35,799	61,050
U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,544
Gross Unrealized Gains	0
Gross Unrealized Losses	(24)
Fair Value	10,520	0
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,645	1,800
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 3,645	$ 1,800