Marketable Securities - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Financial Instruments And Marketable Securities [Abstract]
Dollar value of transfers between levels	$ 0	$ 0	$ 0	$ 0