Balance Sheet Components - Marketable Securities (Details)	6 Months Ended
	Jun. 30, 2016 USD ($) security	Dec. 31, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 292,553,000
Unrealized Gains	323,000
Unrealized Losses	(116,000)
Fair Value	292,760,000	$ 0
Other-than-temporary losses	$ 0
Securities in an unrealized loss position, greater than or equal to one year | security	0
Maximum maturity of marketable securities	2 years
Commercial Paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 17,924,000
Unrealized Gains	51,000
Unrealized Losses	0
Fair Value	17,975,000
U.S. government notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	125,398,000
Unrealized Gains	37,000
Unrealized Losses	(11,000)
Fair Value	125,424,000
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	149,231,000
Unrealized Gains	235,000
Unrealized Losses	(105,000)
Fair Value	$ 149,361,000