Debt Security Investments (Tables)

6 Months Ended

Jun. 30, 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):

	June 30, 2012									December 31, 2011
(in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
U.S. Treasury securities	$	83,492	$	—	$	(45	)	$	83,447	$	33,481	$	—	$	(2	)	$	33,479

Amortized cost and the fair value of debt security investments, by contractual maturity

The following table presents the amortized cost and the fair value of debt security investments, by contractual maturity (in thousands):

	June 30, 2012
(in thousands)	Amortized Cost		Fair Value
Due in one year or less	$	55,092	$	55,070
Due after one year through five years		28,400		28,377
Total securities held to maturity	$	83,492	$	83,447