Cash, Cash Equivalents, and Investments - Gross Unrealized Losses and Fair Values for Available-for-Sale Investments (Detail) $ in Thousands	Jun. 30, 2019 USD ($)
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	$ 61,379
Unrealized losses, less than 12 months	(138)
Fair value, 12 months or greater	66,900
Unrealized losses, 12 months or greater	(129)
Total fair value	128,279
Total unrealized losses	(267)
Treasury Bills
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	24,855
Unrealized losses, less than 12 months	(20)
Fair value, 12 months or greater	0
Unrealized losses, 12 months or greater	0
Total fair value	24,855
Total unrealized losses	(20)
Agency Bonds
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	5,903
Unrealized losses, less than 12 months	(27)
Fair value, 12 months or greater	0
Unrealized losses, 12 months or greater	0
Total fair value	5,903
Total unrealized losses	(27)
Corporate Bonds
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	26,243
Unrealized losses, less than 12 months	(90)
Fair value, 12 months or greater	42,031
Unrealized losses, 12 months or greater	(86)
Total fair value	68,274
Total unrealized losses	(176)
Asset-Backed Securities
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	4,378
Unrealized losses, less than 12 months	(1)
Fair value, 12 months or greater	21,331
Unrealized losses, 12 months or greater	(36)
Total fair value	25,709
Total unrealized losses	(37)
Sovereign Bonds
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	0
Unrealized losses, less than 12 months	0
Fair value, 12 months or greater	2,689
Unrealized losses, 12 months or greater	(1)
Total fair value	2,689
Total unrealized losses	(1)
Municipal Bonds
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	0
Unrealized losses, less than 12 months	0
Fair value, 12 months or greater	849
Unrealized losses, 12 months or greater	(6)
Total fair value	849
Total unrealized losses	$ (6)