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License, Clinical Trial and Sponsored Research Agreements (Details Textual) - USD ($) |  |  | 1 Months Ended | 12 Months Ended |  |  |  |
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Aug. 02, 2018 | Jul. 03, 2017 | Nov. 30, 2017 | Nov. 20, 2017 | May 31, 2017 | Mar. 17, 2017 | Feb. 28, 2017 | Oct. 31, 2016 | Apr. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2018 | Dec. 31, 2017 | Mar. 17, 2018 | Jan. 03, 2018 | Nov. 28, 2017 | Dec. 31, 2016
Payment Of Upfront Fees |  |  |  |  | $ 600,000 |  |  |  |  |  |  |  |  |  |  |
Revenue Recognition Milestone Method Payments Due | $ 13,500,000 |  |  |  | 14,900,000 |  |  |  |  |  |  |  |  |  |  |
Research And Development Expense, Sponsored Research Payment |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 800,000 |
Research and Development Expense |  |  |  |  |  |  |  |  |  |  | $ 2,100,000 |  |  |  |  |
Stock Issued During Period, Value, Purchase of Assets |  |  |  |  |  |  |  |  |  |  |  | $ 1,682,000 |  |  |  |
Proceeds from Issuance of Private Placement |  |  |  |  |  |  |  | $ 10,000,000 |  |  |  |  |  |  |  |
Common Stock, Shares Authorized |  |  |  |  |  |  |  |  |  |  | 50,000,000 | 50,000,000 |  |  |  |
Research and development - licenses acquired |  |  |  |  |  |  |  |  |  |  | $ 3,360,000 | $ 12,433,000 |  |  |  |
Cost of Goods and Services Sold |  |  |  |  | 50,000 |  |  |  |  |  |  |  |  |  |  |
UCLA License [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and Development Expense |  |  |  |  |  |  |  |  |  |  | 100,000 | 100,000 |  |  |  |
Research and development - licenses acquired |  |  |  |  |  |  |  |  |  |  | 0 | 200,000 |  |  |  |
Psca Technology License [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payment Of Upfront Fees |  |  |  |  | 300,000 |  |  |  |  |  |  |  |  |  |  |
Revenue Recognition Milestone Method Payments Due |  |  |  |  | 14,900,000 |  |  |  |  |  |  |  |  |  |  |
Research and development - licenses acquired |  |  |  |  |  |  |  |  |  |  | 0 | 300,000 |  |  |  |
Cost of Goods and Services Sold |  |  |  |  | 50,000 |  |  |  |  |  |  |  |  |  |  |
Cs Technology License [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payment Of Upfront Fees |  |  |  |  | 600,000 |  |  |  |  |  |  |  |  |  |  |
Revenue Recognition Milestone Method Payments Due |  |  |  |  | 14,900,000 |  |  |  |  |  |  |  |  |  |  |
Research and development - licenses acquired |  |  |  |  |  |  |  |  |  |  | 0 | 600,000 |  |  |  |
Cost of Goods and Services Sold |  |  |  |  | $ 50,000 |  |  |  |  |  |  |  |  |  |  |
IL13Ra2 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and Development Expense |  |  |  |  |  |  |  |  |  |  | 1,100,000 | 1,400,000 |  |  |  |
Harvard College License [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payment Of Upfront Fees |  |  | $ 300,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Other Commitment, Due in Next Twelve Months |  |  |  | $ 25,000 |  |  |  |  |  |  |  |  |  |  |  |
Other Commitment, Due in Third Year |  |  |  | 100,000 |  |  |  |  |  |  |  |  |  |  |  |
Other Commitment, Due in Second Year |  |  |  | 50,000 |  |  |  |  |  |  |  |  |  |  |  |
Development Milestones Method Additional Payments Due |  |  |  | 16,700,000 |  |  |  |  |  |  |  |  |  |  |  |
Cost of Goods and Services Sold |  |  |  | $ 25,000 |  |  |  |  |  |  |  |  |  |  |  |
Sponsored Research Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and Development Expense |  |  |  |  |  |  |  |  |  |  | 2,000,000 | 2,000,000 |  |  |  |
CD123 CRA [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and Development Expense |  |  |  |  |  |  |  |  |  |  | 800,000 | 1,400,000 |  |  |  |
St Jude XSCID [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and development - licenses acquired |  |  |  |  |  |  |  |  |  |  | 1,000,000 | 0 |  |  |  |
Cost of Goods and Services Sold | $ 100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
University of California [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Development Milestones Method Additional Payments Due |  |  |  |  |  | $ 14,300,000 |  |  |  |  |  |  |  |  |  |
University of California [Member] | UCLA License [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payment Of Upfront Fees |  |  |  |  |  | 200,000 |  |  |  |  |  |  |  |  |  |
Other Commitment, Due in Next Twelve Months |  |  |  |  |  | 15,000 |  |  |  |  |  |  |  |  |  |
Other Commitment, Due in Fifth Year |  |  |  |  |  | 50,000 |  |  |  |  |  |  |  |  |  |
Other Commitment, Due in Fourth Year |  |  |  |  |  | $ 25,000 |  |  |  |  |  |  |  |  |  |
City Of Hope [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payment Of Upfront Fees |  |  |  |  |  |  | $ 100,000 |  |  |  |  |  |  |  |  |
Revenue Recognition Milestone Method Payments Due |  |  |  |  |  |  | 100,000 |  |  |  |  |  |  |  |  |
Research And Development Expense, Sponsored Research Payment |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 900,000 |  |
City Of Hope [Member] | Intellectual Property [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payment Of Upfront Fees |  |  |  |  |  |  |  |  | $ 2,000,000 |  |  |  |  |  |  |
Revenue Recognition Milestone Method Payments Due |  |  |  |  |  |  |  |  |  |  |  | 2,000,000 |  |  |  |
City Of Hope [Member] | Intellectual Property [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Royalty Expense |  |  |  |  |  |  |  |  |  |  |  | 1,000,000 |  |  |  |
City Of Hope [Member] | Commitment Two [Member] | Intellectual Property [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Development Milestones Method Additional Payments Due |  |  |  |  |  |  |  |  |  | $ 14,500,000 |  |  |  |  |  |
City Of Hope [Member] | AR CD123 License [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue Recognition Milestone Method Payments Due |  |  |  |  |  |  | 14,500,000 |  |  |  |  |  |  |  |  |
City Of Hope [Member] | IL License [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cost of Goods and Services Sold |  |  |  |  |  |  | 25,000 |  |  |  |  |  |  |  |  |
City Of Hope [Member] | Spacer License [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cost of Goods and Services Sold |  |  |  |  |  |  | 10,000 |  |  |  |  |  |  |  |  |
City Of Hope [Member] | IL13Ra2 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payment Of Upfront Fees |  |  |  |  |  |  | 9,300 |  |  |  |  |  |  |  |  |
Revenue Recognition Milestone Method Payments Due |  |  |  |  |  |  | 14,500,000 |  |  |  |  |  |  |  |  |
Research And Development Expense, Sponsored Research Payment |  |  |  |  |  |  | 200,000 |  |  |  |  |  |  |  |  |
Licensing Arrangements Additional Costs Incurred |  |  |  |  |  |  | 100,000 |  |  |  |  |  |  |  |  |
Cost of Goods and Services Sold |  |  |  |  |  |  | 25,000 |  |  |  |  |  |  |  |  |
City Of Hope [Member] | CD123 CRA [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payment Of Upfront Fees |  |  |  |  |  |  | 19,450 |  |  |  |  |  |  |  |  |
Research And Development Expense, Sponsored Research Payment |  |  |  |  |  |  | 200,000 |  |  |  |  |  |  |  |  |
Licensing Arrangements Additional Costs Incurred |  |  |  |  |  |  | $ 97,490 |  |  |  |  |  |  |  |  |
City Of Hope [Member] | Patent and Know-how Rights [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research And Development Expense, Sponsored Research Payment |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 75,000 |  |
Fred Hutchinson Cancer Research Center [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research And Development Expense, Sponsored Research Payment |  |  |  |  |  |  |  |  |  |  |  |  | $ 600,000 |  |  |
Fred Hutchinson Cancer Research Center [Member] | CD20 Technology License [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payment Of Upfront Fees |  | $ 300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Development Milestones Method Additional Payments Due |  | 39,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cost of Goods and Services Sold |  | 50,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fred Hutchinson Cancer Research Center [Member] | CD20 Clinical Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research And Development Expense, Sponsored Research Payment |  | $ 5,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and Development Expense |  |  |  |  |  |  |  |  |  |  | $ 1,300,000 | 600,000 |  |  |  |
Common Class A [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Value, Purchase of Assets |  |  |  |  |  |  |  |  |  |  |  | $ 0 |  |  |  |
Common Stock, Shares Authorized |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,000,000
Common Class A [Member] | City Of Hope [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, Purchase of Assets |  |  |  |  |  |  |  | 293,588 |  |  |  |  |  |  |  |
Common Class A [Member] | City Of Hope [Member] | Valuation, Market Approach [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Granted During Period, Value Per Share Determined |  |  |  |  |  |  |  | $ 5.73 |  |  |  |  |  |  |  |
Stock Issued During Period, Value, Purchase of Assets |  |  |  |  |  |  |  | $ 1,700,000 |  |  |  |  |  |  |  |
Common Class A [Member] | City Of Hope [Member] | Intellectual Property [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and Development Expense |  |  |  |  |  |  |  |  |  | $ 1,000,000 |  |  |  |  |  |
Stock Granted During Period, Valuation Inputs, Weighted Marketability Rate |  |  |  |  |  |  |  |  |  | 44.80% |  |  |  |  |  |
Stock Granted During Period, Valuation Inputs, Weighted Average Cost of Capital |  |  |  |  |  |  |  |  |  | 30.00% |  |  |  |  |  |
Common Class A [Member] | City Of Hope [Member] | Intellectual Property [Member] | Discounted Cash Flow Model [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Granted During Period, Value Per Share Determined |  |  |  |  |  |  |  |  |  | $ 0.147 |  |  |  |  |  |
Stock Issued During Period, Value, Purchase of Assets |  |  |  |  |  |  |  |  |  | $ 100,000 |  |  |  |  |  |

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