Cash and Cash Equivalents and Investments (Tables)

12 Months Ended

Dec. 31, 2013

Cash and Cash Equivalents and Investments [Abstract]

Schedule of Cash, Cash Equivalents and Short-term Investments

	As of December 31, 2013
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
			(in thousands)
Cash and cash equivalents	$	37,499	$	—	$	—		$	37,499
Securities maturing within one year:
Certificates of deposit	552		—		—			552
U.S. treasury securities	91,075		3		(1		)	91,077
Total short-term investments	$	91,627	$	3	$	(1	)	$	91,629
Total cash and cash equivalents and investments	$	129,126	$	3	$	(1	)	$	129,128

	As of December 31, 2012
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
			(in thousands)
Cash and cash equivalents	$	30,423	$	—	$	—		$	30,423
Securities maturing within one year:
Certificates of deposit	551		—		—			551
U.S. treasury securities	192,211		24		(1		)	192,234
Total short-term investments	$	192,762	$	24	$	(1	)	$	192,785
Total cash and cash equivalents and investments	$	223,185	$	24	$	(1	)	$	223,208