The Company and Significant Accounting Policies - Summary of Amortized Cost and Unrealized (Gains) Losses of Available for Sale Securities (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Certificates of Deposit
Amortized Cost
Due after one year through five years	$ 8,282
Total	8,282
Unrealized (gains)losses
Due after one year through five years	(34)
Total	(34)
Corporate Bonds
Amortized Cost
Due within a year	60,010
Due after one year through five years	115,953
Total	175,963
Unrealized (gains)losses
Due within a year	(79)
Due after one year through five years	(1,394)
Total	$ (1,473)