Fair Value Measurement - Summary of Contractual Maturities of Available for Sale Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities, contractual maturities less than 1 year	$ 53,727	$ 24,389
Available for sale securities, contractual maturities between 1 to 5 years	174,407	196,990
Available for sale securities, contractual maturities between 5 to 10 years	53,158	55,605
Available for sale securities, contractual maturities, Total	281,292	276,984
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities, contractual maturities less than 1 year	8,986	14,183
Available for sale securities, contractual maturities between 1 to 5 years	145,521	144,894
Available for sale securities, contractual maturities between 5 to 10 years	23,855	22,735
Available for sale securities, contractual maturities, Total	178,362	181,812
U.S. Treasuries [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities, contractual maturities less than 1 year	21,351	4,919
Available for sale securities, contractual maturities between 1 to 5 years	17,208	40,240
Available for sale securities, contractual maturities, Total	38,559	45,159
U.S. Government Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities, contractual maturities less than 1 year	6,924	4,788
Available for sale securities, contractual maturities between 1 to 5 years	6,762	7,031
Available for sale securities, contractual maturities between 5 to 10 years	29,303	32,870
Available for sale securities, contractual maturities, Total	42,989	44,689
Money Market Funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities, contractual maturities less than 1 year	16,416	449
Available for sale securities, contractual maturities, Total	16,416	449
Supranational Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities, contractual maturities between 1 to 5 years	4,766	4,741
Available for sale securities, contractual maturities, Total	4,766	4,741
Asset Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities, contractual maturities between 1 to 5 years	150	84
Available for sale securities, contractual maturities, Total	150	84
Municipal Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Available for sale securities, contractual maturities less than 1 year	50	50
Available for sale securities, contractual maturities, Total	$ 50	$ 50

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 sixth through tenth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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