Cash Cash Equivalents and Marketable Securities - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2015 USD ($) Investment	Jun. 30, 2014 USD ($)
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	5 months 23 days
Number of debt securities in unrealized loss positions | Investment	26
Debt securities in unrealized loss positions, total unrealized loss	$ 4,000
Debt securities in unrealized loss positions, total fair market value	10,144,000
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