Summary of Significant Accounting Policies (Details) - Development phase [Domain]	1 Months Ended											2 Months Ended	12 Months Ended			21 Months Ended	36 Months Ended	40 Months Ended	43 Months Ended	144 Months Ended
	Dec. 31, 2014 USD ($) item	Oct. 31, 2014 USD ($) item	Nov. 30, 2013 USD ($)	Oct. 31, 2013 USD ($)	May. 31, 2013 item	Mar. 31, 2013 USD ($)	Dec. 31, 2011 USD ($) item	Oct. 31, 2010 USD ($) item	Aug. 31, 2008 USD ($)	Dec. 31, 2006 USD ($)	May. 31, 2000 USD ($)	Nov. 30, 2013 item	Jun. 30, 2015 USD ($) item	Jun. 30, 2014 USD ($)	Jun. 30, 2013 USD ($)	Aug. 31, 2008 USD ($)	Oct. 31, 2013 USD ($)	Dec. 31, 2012 item	Jun. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)
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
Average involvement period over which the upfront payments on single-target licenses are amortized													6 years 6 months
Difference between the full cost to manufacture and amounts received from collaborators for preclinical and clinical materials | $													$ 9,200,000	$ 2,300,000	$ 755,000
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
Right-to-test agreement | Minimum
Summary of Significant Accounting Policies
Average period over which upfront payments are deferred and recognized													12 months
Right-to-test agreement | Maximum
Summary of Significant Accounting Policies
Average period over which upfront payments are deferred and recognized													18 months
Janssen | Maytansinoid agent
Summary of Significant Accounting Policies
Payments received under collaboration agreement | $	$ 1,000,000
Amgen | Development and Commercialization License | Exclusive license
Summary of Significant Accounting Policies
Number of single-target licenses													4					3
Amgen | Development and Commercialization License | Non-exclusive license
Summary of Significant Accounting Policies
Number of single-target licenses					1
Bayer HealthCare | Development and Commercialization License | Exclusive license
Summary of Significant Accounting Policies
Number of single-target licenses													1
Biotest | Development and Commercialization License | Exclusive license
Summary of Significant Accounting Policies
Number of single-target licenses													1
Lilly
Summary of Significant Accounting Policies
Payments received under collaboration agreement | $																			$ 28,200,000
Lilly | Development and Commercialization License
Summary of Significant Accounting Policies
Payments received under collaboration agreement | $																			$ 23,500,000
Number of single-target licenses	2
Lilly | Development and Commercialization License | Exclusive license
Summary of Significant Accounting Policies
Number of single-target licenses													3
Lilly | Right-to-test agreement
Summary of Significant Accounting Policies
Payments received under collaboration agreement | $							$ 20,000,000
Number of single-target licenses							3
Novartis
Summary of Significant Accounting Policies
Payments received under collaboration agreement | $																	$ 60,200,000
Novartis | Development and Commercialization License
Summary of Significant Accounting Policies
Payments received under collaboration agreement | $								$ 1,000,000									$ 55,000,000
Number of single-target licenses		3
Number of licenses to two related targets													1
Number of related targets													2
Novartis | Development and Commercialization License | Exclusive license
Summary of Significant Accounting Policies
Payments received under collaboration agreement | $		$ 1,000,000	$ 1,000,000	$ 1,000,000
Number of single-target licenses		3										2	5
Number of related targets													1
Novartis | Right-to-test agreement
Summary of Significant Accounting Policies
Payments received under collaboration agreement | $						$ 1,000,000		$ 45,000,000
Novartis | Right-to-test agreement | Exclusive license
Summary of Significant Accounting Policies
Number of single-target licenses								6
Roche | Development and Commercialization License | Exclusive license
Summary of Significant Accounting Policies
Number of single-target licenses													5
Roche | Development and Commercialization License | Exclusive license | Kadcyla
Summary of Significant Accounting Policies
Payments received under collaboration agreement | $											$ 2,000,000
Sanofi | Development and Commercialization License
Summary of Significant Accounting Policies
Payments received under collaboration agreement | $																				$ 20,500,000
Number of related targets													1
Sanofi | Development and Commercialization License | Exclusive 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
Payments received under collaboration agreement | $									$ 3,500,000	$ 500,000						$ 4,000,000