Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2018

Summary of financial assets and liabilities measured on recurring basis

	September 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	$	17,880	$	—	$	—	$	17,880	$	3,477	$	—	$	—	$	3,477
U.S. Treasury securities		100,468		—		—		100,468		67,026		—		—		67,026
U.S. agency securities		—		18,849		—		18,849		—		27,072		—		27,072
Municipal securities		—		11,574		—		11,574		—		12,149		—		12,149
Total financial assets	$	118,348	$	30,423	$	—	$	148,771	$	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 September 30, 2018	$	—