Balance Sheet Components - Unrealized Gains and Losses and Fair Value of Investments (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) security	Dec. 31, 2015 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 300,362,000
Unrealized Gains	114,000
Unrealized Losses	(566,000)
Fair Value	299,910,000	$ 0
Realized other-than-temporary losses on marketable securities	$ 0	$ 0
Marketable securities in continuous unrealized loss position, greater than twelve months | security	0	0
Maximum maturity of marketable securities	2 years
Commercial Paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 5,962,000
Unrealized Gains	0
Unrealized Losses	0
Fair Value	5,962,000
U.S. government notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	110,945,000
Unrealized Gains	5,000
Unrealized Losses	(194,000)
Fair Value	110,756,000
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	183,455,000
Unrealized Gains	109,000
Unrealized Losses	(372,000)
Fair Value	$ 183,192,000