Marketable Securities (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Marketable Securities [Line Items]
Amortized Cost	$ 4,002,000	$ 9,022,000
Gross Unrealized Gains	3,000	6,000
Gross Unrealized Losses
Fair Value	4,005,000	9,028,000
US Treasury Bills and Notes | Due In One Year Or Less
Marketable Securities [Line Items]
Amortized Cost	2,002,000	9,022,000
Gross Unrealized Gains	1,000	6,000
Gross Unrealized Losses
Fair Value	2,003,000	9,028,000
US Treasury Bills and Notes | Due After One Year Through Two Years
Marketable Securities [Line Items]
Amortized Cost	2,000,000
Gross Unrealized Gains	2,000
Gross Unrealized Losses
Fair Value	$ 2,002,000