Collaborative Arrangements and Licensing Agreements, Alnylam Pharmaceuticals, Inc. (Details) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Mar. 31, 2004 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) Program Target
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue earned		$ 172,299	$ 120,911	$ 104,152	$ 110,304	$ 160,349	$ 110,927	$ 38,470	$ 36,874	$ 507,666	$ 346,620	$ 283,703
Alnylam Pharmaceuticals, Inc. [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Upfront payment recorded as deferred revenue	$ 5,000
Maximum amount of payments receivable per drug for milestone payments		3,400								3,400
Maximum amount of payments receivable per drug for development milestones		1,100								1,100
Maximum amount of payments receivable per drug for regulatory milestones		2,300								2,300
Next prospective milestone		800								800
Maximum amount of payments payable for development and regulatory milestones		3,400								3,400
Number of therapeutic programs | Program												4
Number of therapeutic targets granted to Ionis | Target												4
Number of other unnamed therapeutic targets granted to Ionis | Target												2
Number of therapeutic targets granted by Ionis | Target												4
Cumulative payments received		$ 70,000								70,000
Revenue earned										$ 3,300	$ 1,100	$ 1,300