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Represents range of tiered, double-digit royalty payments on future global sales if product is successfully commercialized.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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License agreements - Mercus (Details) $ / shares in Units, $ in Thousands, shares in Millions		1 Months Ended			12 Months Ended
	Jan. 23, 2017 USD ($) $ / shares	Feb. 28, 2017 USD ($)	Jan. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($)
License agreements
Long term investment				$ 31,987	$ 134,356	$ 31,987
Research and development expense					1,326,361	581,861	$ 479,514
Unrealized Gain (Loss) on Securities					(24,275)	(3,261)	$ (4,581)
Merus
License agreements
Number of independent programs \| item			11
Number of preclinical discovery programs \| item			2
Number of programs under the resulting products are co-funded for development \| item			2
Associated future global development costs , if elected to co-develop (as a percent)			35.00%
Upfront payment under license agreement		$ 120,000
Research and development expense					6,500
Merus \| Accrued and other liabilities
License agreements
Accrued and other liabilities					2,100
Merus \| U.S.
License agreements
Profit sharing (as a percent)			50.00%
Percentage of profit (losses)			50.00%
Merus \| Minimum
License agreements
Royalty payments on future global net sales (as a percent)			6.00%
Merus \| Minimum \| U.S.
License agreements
Royalty payments on future global net sales (as a percent)			6.00%
Merus \| Minimum \| Non-U.S.
License agreements
Royalty payments on future global net sales (as a percent)			6.00%
Merus \| Maximum
License agreements
Number of additional preclinical discovery programs \| item			9
Royalty payments on future global net sales (as a percent)			10.00%
Percentage of reverse royalty			4.00%
Merus \| Maximum \| U.S.
License agreements
Royalty payments on future global net sales (as a percent)			10.00%
Percentage of additional royalties			4.00%
Merus \| Maximum \| Non-U.S.
License agreements
Royalty payments on future global net sales (as a percent)			10.00%
Merus \| Maximum \| Development and Regulatory Milestones
License agreements
Additional milestone payments under the license agreement			$ 100,000
Merus \| Maximum \| Commercialization Milestones
License agreements
Additional milestone payments under the license agreement			$ 250,000
Merus \| Stock purchase agreement
License agreements
Purchase of common stock under Stock Purchase Agreement (in shares ) \| shares				3.2
Purchase price of common stock				$ 80,000		$ 80,000
Per share price \| $ / shares	$ 24.50			$ 25.00		$ 25.00
Standstill period	3 years
Lock-up period	18 months
Percentage of total shares allowed to sell during any 12-month period (as a percent)	33.00%
Percentage of total shares allowed to sell during any three-month period (as a percent)	10.00%
Discount for lack of marketability	$ 5,600
Fair value of shares on the issuance date	72,800
Total consideration paid	$ 80,000
Long term investment					72,800
Research and development expense					7,200
Fair market value of our long term investments					$ 62,100
Ownership percentage (as a percent)					17.00%
Unrealized Gain (Loss) on Securities					$ (10,700)