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

12 Months Ended

Dec. 31, 2013

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, 2013 (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	$	103,262		$	—	$	—		$	103,262
U.S. Treasury securities		239,959			69		(4	)		240,024
Total		343,221			69		(4	)		343,286
Less amounts classified as cash equivalents		(103,262	)		—		—			(103,262	)
Total available-for-sale securities	$	239,959		$	69	$	(4	)	$	240,024

        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