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Note 1 - Nature of the Business and Group Internal Restructuring (Details Textual) $ / shares in Units, ¥ in Thousands, $ in Thousands |  |  |  |  |  | 1 Months Ended | 12 Months Ended |  |  |
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Mar. 14, 2017 USD ($) $ / shares shares | Jul. 20, 2015 USD ($) shares | Jul. 20, 2015 CNY (¥) shares | May 06, 2015 USD ($) | May 06, 2015 CNY (¥) | Apr. 13, 2015 USD ($) $ / shares shares | Mar. 30, 2015 USD ($) | Mar. 30, 2015 CNY (¥) | Sep. 30, 2017 USD ($) | Sep. 30, 2017 CNY (¥) | Sep. 30, 2016 USD ($) $ / shares shares | Aug. 31, 2015 USD ($) | Aug. 31, 2015 CNY (¥) | Apr. 30, 2015 USD ($) shares | Mar. 31, 2015 shares | Jan. 31, 2015 | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2017 CNY (¥) | Jul. 02, 2015 | Dec. 31, 2012
Stock Issued During Period, Value, New Issues |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 89,443 | $ 15,250 | $ 16,000 |  |  |
Shares Issued, Price Per Share | $ / shares | $ 20 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 32,828 | 14,908 |  |  |  |
Cash |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 27,481 | 11,687 |  |  |  |
Liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4,792 | 2,609 |  |  |  |
Proceeds from Issuance of Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 50,505 | $ 15,250 | $ 16,000 |  |  |
Sale to Third-party Investors [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues | shares |  |  |  |  |  |  |  |  |  |  | 1,129,628 |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Value, New Issues |  |  |  |  |  |  |  |  |  |  | $ 15,250 |  |  |  |  |  |  |  |  |  |  |
Shares Issued, Price Per Share | $ / shares |  |  |  |  |  |  |  |  |  |  | $ 13.50 |  |  |  |  |  |  |  |  |  |  |
IPO [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues | shares | 174,286 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares Issued, Price Per Share | $ / shares | $ 20 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Common Stock | $ 47,184 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Private Placement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues | shares | 2,541,048 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mr. Dong Liang [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues | shares |  |  |  |  |  |  |  |  |  |  |  |  |  | 320,000 |  |  |  |  |  |  |  |
Founders [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues | shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 13,429,997 |  |  |  |  |  |  |
Wanchun Biotech [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues | shares |  |  |  |  |  | 100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Wanchun Biotech [Member] | Internal Restructuring Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues | shares |  | 60,000 | 60,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Beijing Sangel Fang Sheng Venture Capital [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues | shares |  |  |  |  |  | 1,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Value, New Issues |  |  |  |  |  | $ 16,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares Issued, Price Per Share | $ / shares |  |  |  |  |  | $ 10 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Nereus Trust [Member] | Private Placement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued in Lieu of Royalty Payments | shares | 2,112,963 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Wanchun Biotech [Member] | Drug Research [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Assets |  | $ 1,513 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash |  | 1,201 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Due from Related Parties |  | 312 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Liabilities |  | 9,705 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shanghai Fosun [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Equity Method Investments |  | $ 1,611 | ¥ 10,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Equity Method Investments, Shares | shares |  | 240,000 | 240,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
One Founder [Member] | Shenzhen Sangel Sino-euro Venture Capital [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Transfer of Stock, Shares | shares |  |  |  |  |  |  |  |  |  |  |  |  |  | 200,000 |  |  |  |  |  |  |  |
Transfer of Stock, Value |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,000 |  |  |  |  |  |  |  |
Wanchun Biotech [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage Sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.00% |  |  |  |  |  |
Equity Method Investment, Ownership Percentage |  | 100.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, Acquisitions | shares |  | 300,000 | 300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
BeyondSpring U.S. [Member] | Wanchun Biotech [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00% |
BeyondSpring U.S. [Member] | Founders [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage |  | 85.02% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Wanchun Pharma [Member] | Wanchun Biotech [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage |  | 9.09% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 90.91%
Equity Method Investment, Ownership Percentage Acquired |  |  |  |  |  |  | 9.09% | 9.09% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Equity Method Investments |  |  |  |  |  |  | $ 1,611 | ¥ 10,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Wanchun Pharma [Member] | Shanghai Fosun [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9.09%
Wanchunbulin [Member] | Wanchun Biotech [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage |  |  |  | 40.00% | 40.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Wanchunbulin [Member] | Wanchun Biotech [Member] | Patents [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Equity Method Investments |  |  |  | $ 5,290 | ¥ 32,800 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Wanchunbulin [Member] | Wanchun Shenzhen [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage |  |  |  | 60.00% | 60.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Equity Method Investments |  |  |  | $ 7,716 | ¥ 49,200 |  |  |  | $ 3,700 | ¥ 25,701 |  | $ 2,000 | ¥ 12,752 |  |  |  |  |  |  |  |  |
Wanchunbulin [Member] | Wanchun Shenzhen [Member] | Investing Additional Capital During the Next 5 Years [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contractual Obligation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,652 |  |  | ¥ 10,747 |  |
Contractual Obligation, Term of Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years |  |  |  |  |
BVI Biotech [Member] | Wanchun Biotech [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00% |

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