Marketable Securities - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2019
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale short-term investments period of contractual maturities	1 year
Available-for-sale long-term investments period of contractual maturities	2 years
Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale long-term investments period of contractual maturities	1 year