Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2017

Summary of financial assets and liabilities measured on recurring basis

	June 30, 2017								December 31, 2016
	Level I		Level II		Level III		Total		Level I		Level II		Level III		Total
	(in thousands)
Financial Assets:
Money market deposits	$	—	$	—	$	—	$	—	$	10,777	$	—	$	—	$	10,777
U.S. Treasury securities		35,084		—		—		35,084		57,442		—		—		57,442
U.S. agency securities		—		46,979		—		46,979		—		56,114		—		56,114
Municipal securities		—		12,925		—		12,925		—		17,304		—		17,304
Total financial assets	$	35,084	$	59,904	$	—	$	94,988	$	68,219	$	73,418	$	—	$	141,637
Current Liabilities:
Warrants	$	—	$	—	$	3,472	$	3,472	$	—	$	—	$	3,792	$	3,792
Total financial liabilities	$	—	$	—	$	3,472	$	3,472	$	—	$	—	$	3,792	$	3,792

Warrants

Rollforward of fair value determined by Level 3 inputs

	Warrants
	(in thousands)
Balance at December 31, 2016	$	3,792
Change in fair value		(320)
Balance at June 30, 2017	$	3,472