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

12 Months Ended

Dec. 31, 2015

Cash, Cash Equivalents and Available for Sale Securities

Summary of available for sale securities, including carrying value and estimated fair values

	As of December 31, 2015
	Cost		Fair Value		Carrying Value		Unrealized Loss
U.S. Treasury securities	$	130,507	$	130,196	$	130,196	$	(311	)
Corporate debt securities		39,995		39,833		39,833		(162	)
Total	$	170,502	$	170,029	$	170,029	$	(473	)

	As of December 31, 2014
	Cost		Fair Value		Carrying Value		Unrealized Loss
U.S. Treasury securities	$	423,859	$	423,746	$	423,746	$	(113	)
Corporate debt securities		—		—		—		—
Total	$	423,859	$	423,746	$	423,746	$	(113	)

Schedule of changes in accumulated other comprehensive income (loss) associated with the unrealized loss on available for sale securities

	Years ended December 31,
	2015			2014
Beginning balance	$	(65	)	$	—
Current period changes in fair value before reclassifications, net of tax		(351	)		(65	)
Amounts reclassified from accumulated other comprehensive income, net of tax		(57	)		—
Total other comprehensive income, net of tax		(408	)		(65	)
Ending balance	$	(473	)	$	(65	)