Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2016

Summary of financial assets and liabilities measured on recurring basis

	December 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	$	10,777	$	—	$	—	$	10,777		$	5,966	$	—	$	—	$	5,966
U.S. Treasury securities		57,442		—		—		57,442			103,813		—		—		103,813
U.S. agency securities		—		56,114		—		56,114			—		78,853		—		78,853
Municipal securities		—		17,304		—		17,304			—		18,920		—		18,920
Total financial assets	$	68,219	$	73,418	$	—	$	141,637		$	109,779	$	97,773	$	—	$	207,552
Current Liabilities:
Warrants	$		$	—	$	3,792	$	3,792		$	—	$	—	$	3,649	$	3,649
Total financial liabilities	$	—	$	—	$	3,792	$	3,792		$	—	$	—	$	3,649	$	3,649

Summary of quantitative information about inputs and valuation methodologies

					Weighted Average
					Interest on
	Fair Value at			Significant	Discount Rate
	December 31, 2016		Valuation Methodology	Unobservable Input	(range, if applicable)
	(in thousands)
Warrants	$	3,792	Black-Scholes Option Pricing Model	Volatility		61.3	%

Warrants

Rollforward of fair value determined by Level 3 inputs

	Warrants
	2016		2015
	(in thousands)
Beginning balance	$	3,649	$	2,232
Warrants exercised		—		(240)
Change in fair value		143		1,657
Ending balance	$	3,792	$	3,649

Long-term Debt

Rollforward of fair value determined by Level 3 inputs

	Term Loan
	2016		2015
	(in thousands)
Beginning balance	$	—	$	20,964
Change in fair value recognized in non-operating expense		—		(964)
Loan payment		—		(20,000)
Ending balance	$	—	$	—