Cash, Cash Equivalents and Available-for-Sale Securities (Tables)

12 Months Ended

Dec. 31, 2012

Cash, Cash Equivalents and Available-for-Sale Securities

Schedule of fair value and amortized cost of cash, cash equivalents, and available-for-sale securities by major security type

As of December 31, 2012 (in thousands):

Cash and cash equivalents and available-for-sale securities	Amortized Cost			Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Cash and money market funds	$	58,605		$	—	$	—	$	58,605
U.S. Treasury securities		155,948			33		—		155,981
Total		214,553			33		—		214,586
Less amounts classified as cash equivalents		(58,605	)		—		—		(58,605	)
Total available-for-sale securities	$	155,948		$	33	$	—	$	155,981

        As of December 31, 2012, all of the Company's available-for-sale securities have a contractual maturity of less than one year.

        As of December 31, 2011 (in thousands):

Cash and cash equivalents and available-for-sale securities	Amortized Cost			Gross Unrealized Gains		Unrealized Losses			Estimated Fair Value
Cash and money market funds	$	38,547		$	—	$	—		$	38,547
U.S. Treasury securities		108,264			27		(2	)		108,289
Total		146,811			27		(2	)		146,836
Less amounts classified as cash equivalents		(39,554	)		—		—			(39,554	)
Total available-for-sale securities	$	107,257		$	27	$	(2	)	$	107,282

Schedule of assets measured at fair value on a recurring basis

The following fair value hierarchy tables present information about the Company's assets (cash and cash equivalents and available-for-sale securities) measured at fair value on a recurring basis, classified as Level 1, as of December 31, 2012 and 2011 (in thousands):

	Balance at December 31, 2012				Balance at December 31, 2011
	Level 1		Total		Level 1		Total
Cash and cash equivalents:
Cash and money market funds	$	58,605	$	58,605	$	38,547	$	38,547
U.S. Treasury securities		—		—		1,007		1,007
Total cash and cash equivalents	$	58,605	$	58,605	$	39,554	$	39,554

	Balance at December 31, 2012				Balance at December 31, 2011
	Level 1		Total		Level 1		Total
Available-for-sale securities:
U.S. Treasury securities	$	155,981	$	155,981	$	107,282	$	107,282
Total available-for-sale securities	$	155,981	$	155,981	$	107,282	$	107,282

	December 31, 2012		December 31, 2011
Reported as:
Cash and cash equivalents	$	58,605	$	39,554
Available-for-sale securities		155,981		107,282
Total	$	214,586	$	146,836