4. Investments

Investments at March 31, 2012 were comprised of the following (in thousands):

	Amortized Cost		Fair Value(1)
Marketable debt securities – current (U.S. Treasury securities, due in less than one year)	$	20,005	$	20,011
Marketable debt securities – non-current (U.S. Treasury securities, due in 12 to 18 months)		10,014		10,029
	$	30,019	$	30,040

Investments at December 31, 2011 were comprised of the following (in thousands):

	Amortized Cost		Fair Value(1)
Marketable debt securities – current (U.S. Treasury securities, due in less than one year)	$	20,004	$	20,020
Marketable debt securities – non-current (U.S. Treasury securities, due in 12 to 18 months)		10,017		10,042
	$	30,021	$	30,062

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(1) See Note 2 for discussion of fair value measurements.

During the three months ended March 31, 2012, there were no sales or maturities of marketable debt securities. In addition, there were no other-than-temporary declines in market value during the three months ended March 31, 2012.