Summary of Significant Accounting Policies (Tables)
 12 Months Ended
Dec. 31, 2014
Summary of Significant Accounting Policies [Abstract]  
Fair Value Measurements for Assets and Liabilities on Recurring Basis
The following table summarizes fair value measurements by level at December 31, 2014 for assets and liabilities measured
at fair value on a recurring basis:

(In thousands)
 
Level I
  
Level II
  
Level III
  
Total
 
Cash equivalents
 $31,159  $—  $—  $31,159 
Short-term investments
  45,622   —   —   45,622 
Warrant liability
  —   —   (5,131)  (5,131)

The following table summarizes fair value measurements by level at December 31, 2013 for assets and liabilities measured
at fair value on a recurring basis:

(In thousands)
 
Level I
  
Level II
  
Level III
  
Total
 
Cash equivalents
 $10,281  $—  $—  $10,281 
Short-term investments
  27,085   —   —   27,085 
Warrant liabilities
  —   —   (24,182)  (24,182)
Changes in Carrying Amounts of Warrant Liabilities
The changes in carrying amounts of warrant liabilities for the years ended December 31, 2014 and 2013 were as follows:
 
(In thousands)
 
2014
  
2013
 
Beginning balance
  24,182   3,972 
Net changes in valuation
  (19,051)  20,210 
Ending balance
  5,131   24,182