Cash, Cash Equivalents and Marketable Securities - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2016 USD ($) Investment	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Cash, cash equivalents and marketable securities [Line Items]
Long-term marketable securities, minimum original maturity term	1 year
Marketable securities, average remaining contractual maturity period	6 months 3 days
Long-term marketable securities	$ 0		$ 1,633,000
Number of debt securities in unrealized loss positions | Investment	3
Debt securities in unrealized loss positions, total unrealized loss	$ 1,000
Debt securities in unrealized loss positions, total fair market value	1,415,000
Credit risk	0
Gain (loss) on investments	$ 0	$ 0
Minimum
Cash, cash equivalents and marketable securities [Line Items]
Short-term marketable securities, minimum original maturity term	90 days