Balance Sheet Components - Marketable Securities (Details)	9 Months Ended
	Sep. 30, 2016 USD ($) security	Dec. 31, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 299,573,000
Unrealized Gains	231,000
Unrealized Losses	(137,000)
Fair Value	299,667,000	$ 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	$ 11,941,000
Unrealized Gains	56,000
Unrealized Losses	0
Fair Value	11,997,000
U.S. government notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	139,509,000
Unrealized Gains	22,000
Unrealized Losses	(32,000)
Fair Value	139,499,000
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	148,123,000
Unrealized Gains	153,000
Unrealized Losses	(105,000)
Fair Value	$ 148,171,000