v3.20.2

Investments - Summary of Investments (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,264,870	$ 1,921,133
Gross Unrealized Gains	17,828	7,735
Gross Unrealized Losses	(529)	(219)
Estimated Fair Value	2,282,169	1,928,649
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	414,613	101,416
Gross Unrealized Gains	521	83
Gross Unrealized Losses	(31)	(9)
Estimated Fair Value	415,103	101,490
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,571,083	1,654,166
Gross Unrealized Gains	15,645	7,360
Gross Unrealized Losses	(493)	(196)
Estimated Fair Value	1,586,235	1,661,330
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	20,077	38,007
Gross Unrealized Gains	21	38
Gross Unrealized Losses	0	0
Estimated Fair Value	20,098	38,045
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	259,097	127,544
Gross Unrealized Gains	1,641	254
Gross Unrealized Losses	(5)	(14)
Estimated Fair Value	$ 260,733	$ 127,784

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