Collaboration and Other Agreements, Janssen Biotech, Inc. (Details) - Janssen Biotech Inc. - USD ($)	1 Months Ended			12 Months Ended
	Jul. 31, 2016	Jan. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	May 31, 2016	Jul. 31, 2015
Janssen MGD011 Agreement
Collaboration and Other Agreements [Line Items]
Sale of common stock (in shares)			1,923,077
Proceeds of stock sale		$ 75,000,000	$ 75,000,000
Nonrefundable upfront payment					$ 50,000,000
Sale of common stock (in dollars per share)		$ 39.00
Premium received on stock purchase		$ 12,300,000
Total consideration		125,000,000
Amount allocated to equity		62,700,000
Amount allocated to license and R&D		62,300,000
Clinical milestone earned during period							$ 10,000,000
Recognized revenue under agreement				$ 2,000,000	$ 72,300,000
Janssen MGD011 Agreement | Maximum
Collaboration and Other Agreements [Line Items]
Potential clinical milestone payments under agreement		205,000,000.0
Potential regulatory milestone payments under agreement		220,000,000.0
Potential sales milestone payments under agreement		$ 150,000,000.0
Janssen MGD015 Agreement
Collaboration and Other Agreements [Line Items]
Nonrefundable upfront payment	$ 75,000,000			75,000,000
Potential clinical milestone payments under agreement						$ 100,000,000.0
Potential regulatory milestone payments under agreement						265,000,000
Potential sales milestone payments under agreement						$ 300,000,000
Recognized revenue under agreement				$ 75,800,000