Cash Cash Equivalents and Marketable Securities - Additional Information (Detail) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2014 Investment	Dec. 31, 2013
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	9 months 14 days
Number of debt securities in unrealized loss positions	24
Debt securities in unrealized loss positions, total unrealized loss	$ 7,600
Debt securities in unrealized loss positions, total fair market value	8,991,000
Credit risk	0
Gain (loss) on investments	$ 0	$ 0
Minimum
Cash, cash equivalents and marketable securities [Line Items]
Marketable securities, minimum original maturity term	90 days