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

9 Months Ended

Sep. 30, 2016

Cash, Cash Equivalents, and Short-term Investments [Abstract]

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

Available for sale securities, including carrying value and estimated fair values, are summarized as follows:

	As of September 30, 2016
	Cost		Unrealized Gains		Unrealized Losses			Fair Value
U.S. Treasury securities	$	120,280	$	47	$	(7	)	$	120,320
Corporate debt securities	35,233		10		(11		)	35,232
Total	$	155,513	$	57	$	(18	)	$	155,552

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

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

The changes in accumulated other comprehensive income (loss) associated with the unrealized gain (loss) on available for sale securities during the three and nine months ended September 30, 2016 and September 30, 2015 were as follows:

	Three months ended September 30,						Nine months ended September 30,
	2016			2015			2016			2015
Beginning balance	$	(118	)	$	24		$	(473	)	$	(65	)
Current period changes in fair value before reclassifications, net of tax	(41		)	85			314			174
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	—			(30		)	—			(30		)
Total other comprehensive income (loss)	(41		)	55			314			144
Ending balance	$	(159	)	$	79		$	(159	)	$	79