Investments - Summary of Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,921,133	$ 1,517,783
Gross Unrealized Gains	7,735	367
Gross Unrealized Losses	(219)	(4,576)
Estimated Fair Value	1,928,649	1,513,574
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	101,416	108,061
Gross Unrealized Gains	83	0
Gross Unrealized Losses	(9)	0
Estimated Fair Value	101,490	108,061
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,654,166	1,233,589
Gross Unrealized Gains	7,360	343
Gross Unrealized Losses	(196)	(4,218)
Estimated Fair Value	1,661,330	1,229,714
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	38,007	73,584
Gross Unrealized Gains	38	1
Gross Unrealized Losses	0	0
Estimated Fair Value	38,045	73,585
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	127,544	102,549
Gross Unrealized Gains	254	23
Gross Unrealized Losses	(14)	(358)
Estimated Fair Value	$ 127,784	$ 102,214

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Publisher FASB
-Name Accounting Standards Codification
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