Cash Cash Equivalents and Marketable Securities - Additional Information (Detail) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Cash, cash equivalents and marketable securities [Line Items]
Marketable securities, average remaining contractual maturity period	9 months 6 days
Number of debt securities in unrealized loss positions	12
Debt securities in unrealized loss positions, total unrealized loss	2,000
Debt securities in unrealized loss positions, total fair market value	9,305,000
Minimum
Cash, cash equivalents and marketable securities [Line Items]
Marketable securities, minimum original maturity term	90 days	90 days
Long-term marketable securities, minimum original maturity term	1 year	1 year