Marketable Securities - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Weighted-average remaining maturity period of marketable debt securities, months	14 months
Minimum
Schedule of Available-for-sale Securities [Line Items]
Remaining maturities of marketable debt securities	2017-10
Maximum
Schedule of Available-for-sale Securities [Line Items]
Remaining maturities of marketable debt securities	2020-09