Marketable Securities - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2012 M
Schedule of Available-for-sale Securities [Line Items]
Debt securities maturities	3 months
Weighted-average remaining maturity period of marketable debt securities, months	11
Minimum
Schedule of Available-for-sale Securities [Line Items]
Remaining maturities of marketable debt securities	2012-11
Maximum
Schedule of Available-for-sale Securities [Line Items]
Remaining maturities of marketable debt securities	2014-12