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

6 Months Ended

Jun. 30, 2017

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 June 30, 2017
	Cost		Unrealized Gains		Unrealized Losses			Fair Value
U.S. Treasury securities	$	48,147	$	—	$	(13	)	$	48,134
Corporate debt securities	7,392		—		(1		)	7,391
Total	$	55,539	$	—	$	(14	)	$	55,525

	As of December 31, 2016
	Cost		Unrealized Gains		Unrealized Losses			Fair Value
U.S. Treasury securities	$	120,288	$	6	$	(33	)	$	120,261
Corporate debt securities	35,114		—		(27		)	35,087
Total	$	155,402	$	6	$	(60	)	$	155,348

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 six months ended June 30, 2017 and June 30, 2016 were as follows:

	Three months ended June 30,						Six months ended June 30,
	2017			2016			2017			2016
Beginning balance	$	(222	)	$	4		$	(212	)	$	(473	)
Current period changes in fair value before reclassifications, net of tax	36			(122		)	26			355
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	—			—			—			—
Total other comprehensive income (loss)	36			(122		)	26			355
Ending balance	$	(186	)	$	(118	)	$	(186	)	$	(118	)