Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 72,568	$ 95,166
Gross Unrealized Gain	108	2
Gross Unrealized Loss	(17)	(283)
Fair Value	72,659	94,885
Money market funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		6,167
Fair Value		6,167
United States government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,028	15,971
Gross Unrealized Gain	5
Gross Unrealized Loss	(3)	(23)
Fair Value	11,030	15,948
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	61,540	73,028
Gross Unrealized Gain	103	2
Gross Unrealized Loss	(14)	(260)
Fair Value	$ 61,629	$ 72,770

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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