Investments (Details) (USD $)	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amount of marketable debt securities, maturities	$ 10,000,000
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable debt securities - due within one year - Amortized cost	20,004,000
Marketable debt securities - due in one to two years - Amortized cost	10,017,000
Marketable debt securities - Amortized cost	30,021,000
Marketable debt securities - due within one year - Fair value	20,020,000
Marketable debt securities - due in one to two years - Fair value	10,042,000
Marketable debt securities - Fair value	$ 30,062,000