Condensed Consolidated Statements of Stockholders' Equity - USD ($)  | 
Total  | 
Employees and Directors [Member]  | 
Common Stock [Member]  | 
 Common Stock [Member]  
Employees and Directors [Member] 
 | 
Additional Paid-in Capital [Member]  | 
 Additional Paid-in Capital [Member]  
Employees and Directors [Member] 
 | 
Accumulated deficit [Member]  | 
 Accumulated deficit [Member]  
Employees and Directors [Member] 
 | 
|---|---|---|---|---|---|---|---|---|
| Balance at Dec. 31, 2016 | $ 99,098,000 | $ 403,000 | $ 431,168,000 | $ (332,473,000) | ||||
| Balance (in shares) at Dec. 31, 2016 | 40,254,457 | |||||||
| Restricted common stock issued to employees and directors | $ 362,000 | $ 0 | $ 362,000 | $ 0 | ||||
| Restricted common stock issued to employees and directors (in shares) | 0 | |||||||
| Stock option compensation expense | 1,492,000 | $ 0 | 1,492,000 | 0 | ||||
| Common stock issued for cash exercise of options | 1,000 | $ 0 | 1,000 | 0 | ||||
| Common stock issued for cash exercise of options (in shares) | 625 | |||||||
| Net loss | (5,247,000) | $ 0 | 0 | (5,247,000) | ||||
| Balance at Mar. 31, 2017 | 95,706,000 | $ 403,000 | 433,023,000 | (337,720,000) | ||||
| Balance (in shares) at Mar. 31, 2017 | 40,255,082 | |||||||
| Balance at Dec. 31, 2016 | 99,098,000 | $ 403,000 | 431,168,000 | (332,473,000) | ||||
| Balance (in shares) at Dec. 31, 2016 | 40,254,457 | |||||||
| Net loss | (13,526,000) | |||||||
| Balance at Jun. 30, 2017 | 89,078,000 | $ 403,000 | 434,674,000 | (345,999,000) | ||||
| Balance (in shares) at Jun. 30, 2017 | 40,286,332 | |||||||
| Balance at Mar. 31, 2017 | 95,706,000 | $ 403,000 | 433,023,000 | (337,720,000) | ||||
| Balance (in shares) at Mar. 31, 2017 | 40,255,082 | |||||||
| Restricted common stock issued to employees and directors | $ 324,000 | $ 0 | $ 324,000 | $ 0 | ||||
| Restricted common stock issued to employees and directors (in shares) | 0 | |||||||
| Stock option compensation expense | 1,243,000 | $ 0 | 1,243,000 | 0 | ||||
| Common stock issued for cash exercise of options | 84,000 | $ 0 | 84,000 | 0 | ||||
| Common stock issued for cash exercise of options (in shares) | 31,250 | |||||||
| Net loss | (8,279,000) | $ 0 | 0 | (8,279,000) | ||||
| Balance at Jun. 30, 2017 | $ 89,078,000 | $ 403,000 | $ 434,674,000 | $ (345,999,000) | ||||
| Balance (in shares) at Jun. 30, 2017 | 40,286,332 |