| Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands | December 2019 Public Offering [Member]  Common Stock [Member] | December 2019 Public Offering [Member]  Additional Paid-in Capital [Member] | December 2019 Public Offering [Member]  AOCI Attributable to Parent [Member] | December 2019 Public Offering [Member]  Retained Earnings [Member] | December 2019 Public Offering [Member] | June 2019 Public Offering [Member]  Common Stock [Member] | June 2019 Public Offering [Member]  Additional Paid-in Capital [Member] | June 2019 Public Offering [Member]  AOCI Attributable to Parent [Member] | June 2019 Public Offering [Member]  Retained Earnings [Member] | June 2019 Public Offering [Member] | The 2019 Share Purchase Agreement [Member]  Common Stock [Member] | The 2019 Share Purchase Agreement [Member]  Additional Paid-in Capital [Member] | The 2019 Share Purchase Agreement [Member]  AOCI Attributable to Parent [Member] | The 2019 Share Purchase Agreement [Member]  Retained Earnings [Member] | The 2019 Share Purchase Agreement [Member] | The 2018 ATM Offering [Member]  Common Stock [Member] | The 2018 ATM Offering [Member]  Additional Paid-in Capital [Member] | The 2018 ATM Offering [Member]  AOCI Attributable to Parent [Member] | The 2018 ATM Offering [Member]  Retained Earnings [Member] | The 2018 ATM Offering [Member] | The 2018 Purchase Agreement [Member]  Common Stock [Member] | The 2018 Purchase Agreement [Member]  Additional Paid-in Capital [Member] | The 2018 Purchase Agreement [Member]  AOCI Attributable to Parent [Member] | The 2018 Purchase Agreement [Member]  Retained Earnings [Member] | The 2018 Purchase Agreement [Member] | The 2017 Purchase Agreement [Member]  Common Stock [Member] | The 2017 Purchase Agreement [Member]  Additional Paid-in Capital [Member] | The 2017 Purchase Agreement [Member]  AOCI Attributable to Parent [Member] | The 2017 Purchase Agreement [Member]  Retained Earnings [Member] | The 2017 Purchase Agreement [Member] | Common Stock [Member] | Additional Paid-in Capital [Member] | AOCI Attributable to Parent [Member] | Retained Earnings [Member] | Total | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Balance (in shares) at Dec. 31, 2017 | 27,502,000 | ||||||||||||||||||||||||||||||||||
| Balance at Dec. 31, 2017 | $ 231,923 | $ 29,365 | $ (4,316) | $ (246,770) | $ 10,202 | ||||||||||||||||||||||||||||||
| Common shares issued (in shares) | 4,086,000 | 4,085,615 | 1,078,000 | 5,232,000 | 5,231,953 | ||||||||||||||||||||||||||||||
| Common shares issued | $ 10,710 | $ 10,710 | $ 2,526 | $ 2,526 | $ 14,995 | $ 14,995 | |||||||||||||||||||||||||||||
| Common shares issued upon exercise of stock options (in shares) | 114,000 | 114,000 | |||||||||||||||||||||||||||||||||
| Common shares issued upon exercise of stock options | $ 415 | (175) | $ 240 | ||||||||||||||||||||||||||||||||
| Common shares issued on redemption of restricted share units (in shares) | 150,000 | ||||||||||||||||||||||||||||||||||
| Common shares issued on redemption of restricted share units | $ 503 | (503) | |||||||||||||||||||||||||||||||||
| Stock-based compensation | 4,276 | 4,276 | |||||||||||||||||||||||||||||||||
| Net loss | (28,868) | (28,868) | |||||||||||||||||||||||||||||||||
| Balance (in shares) at Dec. 31, 2018 | 38,162,000 | ||||||||||||||||||||||||||||||||||
| Balance at Dec. 31, 2018 | $ 261,072 | 32,963 | (4,316) | (275,638) | $ 14,081 | ||||||||||||||||||||||||||||||
| Common shares issued (in shares) | 18,544,000 | 11,500,000 | 1,971,000 | 77,000 | 5,502,000 | 30,043,750 | |||||||||||||||||||||||||||||
| Common shares issued | $ 68,588 | $ 68,588 | $ 19,594 | $ 19,594 | $ 4,730 | $ 4,730 | $ 178 | $ 178 | $ 10,000 | $ 10,000 | |||||||||||||||||||||||||
| Common shares issued upon exercise of stock options (in shares) | 312,000 | 312,000 | |||||||||||||||||||||||||||||||||
| Common shares issued upon exercise of stock options | $ 1,248 | (530) | $ 718 | ||||||||||||||||||||||||||||||||
| Common shares issued on redemption of restricted share units (in shares) | 40,000 | ||||||||||||||||||||||||||||||||||
| Common shares issued on redemption of restricted share units | $ 80 | (80) | |||||||||||||||||||||||||||||||||
| Stock-based compensation | 2,296 | 2,296 | |||||||||||||||||||||||||||||||||
| Other comprehensive gain (loss) | 18 | 18 | |||||||||||||||||||||||||||||||||
| Net loss | (26,277) | (26,277) | |||||||||||||||||||||||||||||||||
| Balance (in shares) at Dec. 31, 2019 | 76,108,000 | ||||||||||||||||||||||||||||||||||
| Balance at Dec. 31, 2019 | $ 365,490 | $ 34,649 | $ (4,298) | $ (301,915) | $ 93,926 |