Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2015

Fair Value Measurements

Schedule of financial instruments measured at fair value by level within fair value hierarchy

	Level 1		Level 2		Level 3
2015
Assets:
Cash equivalents	$	34,324	$	—	$	—
Total assets at fair value	$	34,324	$	—	$	—
Liabilities:
Common stock warrants		—		—		406
Total liabilities at fair value	$	—	$	—	$	406

	Level 1		Level 2		Level 3
2014
Assets:
Cash equivalents	$	40,135	$	—	$	—
Total assets at fair value	$	40,135	$	—	$	—
Liabilities:
Common stock warrants		—		—		296
Total liabilities at fair value	$	—	$	—	$	296

Rollforward of fair value of Level 3 warrants

Beginning balance at December 31, 2012	$	563
Change in fair value		81
Ending balance at December 31, 2013		644
Expiration of Series A-1 and Series A-2 warrants		(493	)
Change in fair value		145
Ending balance at December 31, 2014		296
Change in fair value		110
Ending balance at December 31, 2015	$	406