Debt Security Investments (Tables)

12 Months Ended

Dec. 31, 2012

Debt Security Investments [Abstract]

Amortized cost, gross unrealized gains, gross unrealized losses and the fair value of debt security investments

The following table summarizes amortized cost, gross unrealized gains, gross unrealized losses and the fair value of debt security investments (in thousands):

	December 31, 2012								December 31, 2011
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
U.S. Treasury securities	$	3,486	$	13	$	—	$	3,499	$	36,950	$	—	$	(6)	$	36,944

Gross unrealized losses and fair value of all available for sale debt security investments

	Less than 12 months
	Fair value		Unrealized gains  (losses)
December 31, 2012
U.S. Treasury securities	$	3,499	$	13