Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2018

Summary of financial assets and liabilities measured on recurring basis

	June 30, 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	$	569	$	—	$	—	$	569	$	3,477	$	—	$	—	$	3,477
U.S. Treasury securities		36,865		—		—		36,865		67,026		—		—		67,026
U.S. agency securities		—		22,332		—		22,332		—		27,072		—		27,072
Municipal securities		—		11,704		—		11,704		—		12,149		—		12,149
Total financial assets	$	37,434	$	34,036	$	—	$	71,470	$	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
	(in thousands)
Balance at December 31, 2017	$	2,644
Change in fair value		4,119
Warrants exercised		(6,763)
Balance at June 30, 2018	$	—