Fair value Measurements - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2015 Security
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]
Available-for-sale investments contractual maturity period	2 years
Available-for-sale investments in gross unrealized loss position	32
Available-for-sale investments in gross unrealized loss position	12 months