Available-for-Sale Marketable Securities - Schedule of Amortized Cost and Fair Values of Marketable Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Amortized Cost of marketable debt securities, contractual maturity, less than one year	$ 45,331		$ 45,331		$ 136,565
Amortized Cost of marketable debt securities, contractual maturity, One year to two years	10,400		10,400		63,125
Amortized Cost	55,731		55,731		199,690
Fair value of marketable debt securities, contractual maturities, less than one year	45,588		45,588		136,701
Fair value of marketable debt securities, contractual maturity, One year to two years	10,506		10,506		63,159
Total fair Value of marketable debt securities, contractual maturity	56,094		56,094		199,860
Proceeds from sale of available-for-sale marketable securities	12,471	$ 0	23,148	$ 0
Realized gain (loss)	66		126
Interest receivable	$ 365		$ 365		$ 971

Amortized cost 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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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in remainder of current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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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), with single maturity date and allocated without single maturity date, maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of realized gain (loss) 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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Carrying amount as of the balance sheet date of current interest earned but not received. Also called accrued interest or accrued interest receivable. For classified balance sheets, represents the current amount receivable, that is amounts expected to be collected within one year or the normal operating cycle, if longer.

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Amount of cash inflow from sale 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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