Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2015

Summary of financial assets and liabilities measured on recurring basis

	December 31, 2015								December 31, 2014
	Level I		Level II		Level III		Total		Level I		Level II		Level III		Total
	(in thousands)
Financial Assets:
Money market deposits	$	5,966	$	—	$	—	$	5,966	$	—	$	—	$	—	$	—
U.S. Treasury securities		103,813		—		—		103,813		—		—		—		—
U.S. agency securities		—		78,853		—		78,853		—		—		—		—
Municipal securities		—		18,920		—		18,920
Total financial assets	$	109,779	$	97,773	$	—	$	207,552	$	—	$	—	$	—	$	—
Current Liabilities:
Warrants	$	—	$	—	$	3,649	$	3,649	$	—	$	—	$	2,232	$	2,232
Long-term Liabilities:
Senior secured term loan	$	—	$	—	$	—	$	—	$	—	$	—	$	20,964	$	20,964
Total financial liabilities	$	—	$	—	$	3,649	$	3,649	$	—	$	—	$	23,196	$	23,196

Summary of quantitative information about inputs and valuation methodologies

					Weighted Average
					Interest on
	Fair Value at			Significant	Discount Rate
	December 31, 2015		Valuation Methodology	Unobservable Input	(range, if applicable)
	(in thousands)				(in thousands)
—Warrants	$	3,649	Black-Scholes Option Pricing Model	Volatility		79.6	%

Warrants

Rollforward of fair value determined by Level 3 inputs

	Warrants
	2015		2014
	(in thousands)
Beginning balance	$	2,232	$	568
Warrants exercised		(240)		—
Change in fair value		1,657		1,664
Ending balance	$	3,649	$	2,232

Long-term Debt

Rollforward of fair value determined by Level 3 inputs

	Term Loan
	2015		2014
	(in thousands)
Beginning balance	$	20,964	$	21,082
Change in fair value recognized in non-operating expense		(964)		(118)
Loan payment		(20,000)		—
Ending balance	$	—	$	20,964