Preferred Stock and Stockholders' Equity (Narrative) (Details)
 1 Months Ended 12 Months Ended
Feb. 26, 2016
shares
Feb. 18, 2015
shares
Jul. 06, 2012
USD ($)
$ / shares
shares
Mar. 29, 2012
$ / shares
shares
Mar. 31, 2015
USD ($)
shares
May. 31, 2014
shares
Mar. 31, 2008
shares
Dec. 31, 2015
USD ($)
item
$ / shares
shares
Dec. 31, 2014
USD ($)
$ / shares
shares
Dec. 31, 2013
USD ($)
shares
Dec. 31, 2012
USD ($)
$ / shares
shares
Dec. 31, 2008
USD ($)
Apr. 30, 2010
shares
Shareholders Equity [Line Items]                          
Preferred stock, shares authorized               10,000,000 10,000,000        
Preferred stock, par value | $ / shares               $ 0.001 $ 0.001        
Preferred stock, shares outstanding               0 0        
Stock and warrants issued during period             8,900,000            
Common stock issued during period upon exercise of warrants                     216,000    
Warrants to purchase common stock             4,500,000            
Common stock, shares issued     11,000,000                    
Common stock, price per share | $ / shares     $ 4.49                    
Net sales from sale of common stock | $     $ 46,100,000                    
Proceeds generated | $                     $ 470,000    
Percentage of liquidated damages                       5.00%  
Number of additional shares authorized for issuance               4,056,000 3,993,000 3,992,000      
Number of stock option plans | item               2          
Number of shares issuable               10,639,000          
Shares available for future grants               8,070,000 7,546,000 4,926,000 4,055,000    
Total intrinsic value of options exercised | $               $ 5,500,000 $ 3,000,000 $ 55,000      
Fair value of options vested | $               $ 5,400,000 4,600,000 5,000,000      
Forfeiture rate, stock option expense               0.00%          
Non-cash stock-based compensation expense | $               $ 6,013,000 $ 5,201,000 $ 5,196,000      
Common shares issued upon exercise of options               2,041,000 1,381,000 35,000      
Other Non-Operating Expense [Member]                          
Shareholders Equity [Line Items]                          
Liquidated damages | $                       $ 1,300,000  
2004 Equity Incentive Plan                          
Shareholders Equity [Line Items]                          
Shares available for future grants                     0    
2012 Stock Option Plan                          
Shareholders Equity [Line Items]                          
Number of additional shares authorized for issuance   4,100,000                      
Increase in shares available for issuance based on percentage of common stock outstanding   4.00%                      
Shares available for future grants                     5,300,000    
2012 Equity Incentive Award Plan                          
Shareholders Equity [Line Items]                          
Increase in shares available for issuance based on percentage of common stock outstanding               4.00%          
Minimum                          
Shareholders Equity [Line Items]                          
Exercise price of warrants | $ / shares                     $ 1.66    
Minimum | 2004 Equity Incentive Plan                          
Shareholders Equity [Line Items]                          
Exercise price as percentage of fair value of common stock               100.00%          
Stock options, vesting period               1 year          
Minimum | 2012 Stock Option Plan                          
Shareholders Equity [Line Items]                          
Exercise price as percentage of fair value of common stock               100.00%          
Stock options, vesting period               1 year          
Maximum                          
Shareholders Equity [Line Items]                          
Exercise price of warrants | $ / shares                     $ 2.96    
Maximum | 2004 Equity Incentive Plan                          
Shareholders Equity [Line Items]                          
Stock options, vesting period               5 years          
Maximum | 2012 Stock Option Plan                          
Shareholders Equity [Line Items]                          
Stock options, vesting period               4 years          
Non-employee [Member]                          
Shareholders Equity [Line Items]                          
Number of awards outstanding | item               1          
Non-cash stock-based compensation expense | $               $ 87,000 $ 470,000 $ 127,000      
Unvested shares               17,000          
Subsequent Events | 2012 Equity Incentive Award Plan                          
Shareholders Equity [Line Items]                          
Number of additional shares authorized for issuance 4,400,000                        
Employee And Director Stock Option                          
Shareholders Equity [Line Items]                          
Non-cash stock-based compensation expense | $               $ 6,000,000 $ 4,700,000 $ 5,100,000      
Unrecognized compensation expense | $               $ 12,700,000          
Unrecognized compensation expense, weighted-average vesting period               2 years 10 months 6 days          
Private Placement 2008 [Member]                          
Shareholders Equity [Line Items]                          
Warrant exercised on a cashless net-exercise basis           529,567              
Common stock issued during period upon exercise of warrants           164,666              
April 2010 Private Placement                          
Shareholders Equity [Line Items]                          
New warrants sold to purchase shares of common stock                         4,200,000
Common stock issued during period upon exercise of warrants       4,200,000                  
Exercise price of warrants | $ / shares       $ 2.96                  
April 2010 and March 2012 Private Placements                          
Shareholders Equity [Line Items]                          
Proceeds generated | $               $ 12,800,000          
Private Placement                          
Shareholders Equity [Line Items]                          
Common stock issued during period upon exercise of warrants         6,200,000                
Exercise price of warrants | $ / shares       $ 4.05                  
Number Of Private Placement Transactions | item               2          
Proceeds generated | $         $ 17,100,000                
Related Parties | March 2012 Private Placement                          
Shareholders Equity [Line Items]                          
Percentage of securities sold to related parties               40.00%          
Directors [Member] | Private Placement                          
Shareholders Equity [Line Items]                          
Common stock issued during period upon exercise of warrants         3,100,000                
Proceeds generated | $         $ 5,900,000