Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2018

Summary of financial assets and liabilities measured on recurring basis

	December 31, 2018								December 31, 2017
	Level I		Level II		Level III		Total		Level I		Level II		Level III		Total
	(in thousands)
Financial Assets:
Money market deposits	$	26,539	$	—	$	—	$	26,539	$	3,477	$	—	$	—	$	3,477
U.S. Treasury securities		75,685		—		—		75,685		67,026		—		—		67,026
U.S. agency securities		—		12,891		—		12,891		—		27,072		—		27,072
Municipal securities		—		18,885		—		18,885		—		12,149		—		12,149
Total financial assets	$	102,224	$	31,776	$	—	$	134,000	$	70,503	$	39,221	$	—	$	109,724
Current Liabilities:
Warrants	$		$	—	$	—	$	—	$	—	$	—	$	2,644	$	2,644
Total financial liabilities	$	—	$	—	$	—	$	—	$	—	$	—	$	2,644	$	2,644

Warrants

Rollforward of fair value determined by Level 3 inputs

	Warrants
	2018		2017
	(in thousands)
Beginning balance	$	2,644	$	3,792
Warrants exercised		(6,762)		—
Change in fair value		4,118		(1,148)
Ending balance	$	—	$	2,644