Marketable Securities - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2015
Schedule of Available-for-sale Securities [Line Items]
Weighted-average remaining maturity period of marketable debt securities, months	16 months
Minimum
Schedule of Available-for-sale Securities [Line Items]
Remaining maturities of marketable debt securities	2015-10
Maximum
Schedule of Available-for-sale Securities [Line Items]
Remaining maturities of marketable debt securities	2018-09