Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2016

Summary of financial assets and liabilities measured on recurring basis

	March 31, 2016								December 31, 2015
	Level I		Level II		Level III		Total		Level I		Level II		Level III		Total
	(in thousands)
Financial Assets:
Money market deposits	$	8,263	$	—	$	—	$	8,263	$	5,966	$	—	$	—	$	5,966
U.S. Treasury securities		103,096		—		—		103,096		103,813		—		—		103,813
U.S. agency securities		—		74,616		—		74,616		—		78,853		—		78,853
Municipal securities		—		18,885		—		18,885		—		18,920		—		18,920
Total financial assets	$	111,359	$	93,501	$	—	$	204,860	$	109,779	$	97,773	$	—	$	207,552
Current Liabilities:
Warrants	$	—	$	—	$	3,139	$	3,139	$	—	$	—	$	3,649	$	3,649
Total financial liabilities	$	—	$	—	$	3,139	$	3,139	$	—	$	—	$	3,649	$	3,649

Warrants

Rollforward of fair value determined by Level 3 inputs

	Warrants
	(in thousands)
Balance at December 31, 2015	$	3,649
Change in fair value		(510)
Balance at March 31, 2016	$	3,139