Summary of Significant Accounting Policies - Revenue (Details) $ in Millions	1 Months Ended						12 Months Ended
	Dec. 31, 2015 item	Mar. 31, 2015 item	Oct. 31, 2014 item	Dec. 31, 2013 item	May 31, 2013 item	Mar. 31, 2013 item	Jun. 30, 2016 USD ($) item	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2011 item	Dec. 31, 2010 item	Dec. 31, 2000 item
Summary of Significant Accounting Policies
Number of types of licensing and development agreements with collaborative partners							2
Development and Commercialization License
Summary of Significant Accounting Policies
Difference between the full cost to manufacture and amounts received from collaborators for preclinical and clinical materials | $							$ 6.9	$ 9.2	$ 2.3
Number of types of milestone payments under collaborative arrangements							3
Number of quarters in arrear for revenue recognition							1
Development and Commercialization License | Minimum
Summary of Significant Accounting Policies
Period to earn royalty payments							10 years
Development and Commercialization License | Maximum
Summary of Significant Accounting Policies
Period to earn royalty payments							12 years
Development and Commercialization License | Kadcyla | Minimum
Summary of Significant Accounting Policies
Period to earn royalty payments							10 years
Development and Commercialization License | Kadcyla | Maximum
Summary of Significant Accounting Policies
Period to earn royalty payments							12 years
Amgen | Exclusive Development And Commercialization License
Summary of Significant Accounting Policies
Number of single-target licenses							2
Amgen | Exclusive Development And Commercialization License | Oxford BioTherapeutics Ltd Member
Summary of Significant Accounting Policies
Number of single-target licenses							1
Amgen | Development and Commercialization License
Summary of Significant Accounting Policies
Number of single-target licenses	4				1		2					3
Bayer | Exclusive Development And Commercialization License
Summary of Significant Accounting Policies
Number of single-target licenses							1
Biotest | Exclusive Development And Commercialization License
Summary of Significant Accounting Policies
Number of single-target licenses							1
CytomX
Summary of Significant Accounting Policies
Number of single-target licenses							1
Lilly | Exclusive Development And Commercialization License
Summary of Significant Accounting Policies
Number of single-target licenses							3
Lilly | Right-to-test agreement
Summary of Significant Accounting Policies
Number of single-target licenses										3
Novartis
Summary of Significant Accounting Policies
Number of related targets							2
Novartis | Exclusive Development And Commercialization License
Summary of Significant Accounting Policies
Number of single-target licenses							5
Number of licenses to two related targets							1
Number of related targets							1
Novartis | Development and Commercialization License
Summary of Significant Accounting Policies
Number of single-target licenses			3
Novartis | Right-to-test agreement
Summary of Significant Accounting Policies
Number of single-target licenses						1					6
Number of related targets						2
Roche | Exclusive Development And Commercialization License
Summary of Significant Accounting Policies
Number of single-target licenses							5
Sanofi | Exclusive Development And Commercialization License
Summary of Significant Accounting Policies
Number of single-target licenses							1
Number of licenses to multiple individual targets							1
Sanofi | Right-to-test agreement
Summary of Significant Accounting Policies
Number of single-target licenses				1
Takeda
Summary of Significant Accounting Policies
Number of single-target licenses							1
Takeda | Right-to-test agreement
Summary of Significant Accounting Policies
Number of single-target licenses		2