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

12 Months Ended

Dec. 31, 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 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

	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 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 for the years ended December 31, 2016 and December 31, 2015 were as follows:

	Years ended December 31,
	2016			2015
Beginning balance	$	(473	)	$	(65	)
Current period changes in fair value before reclassifications, net of tax	261			(351		)
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	—			(57		)
Total other comprehensive income (loss)	261			(408		)
Ending balance	$	(212	)	$	(473	)