Summary of Significant Accounting Policies (Details) (USD $)	1 Months Ended			12 Months Ended
	Jul. 31, 2012	May 31, 2011	May 31, 2010	Jun. 30, 2012 item	Jun. 30, 2011	Jun. 30, 2010
Subsequent Events
Issuance of common stock through a public offering (in shares)	6,250,000	7,800,000	10,350,000
Price at which common stock is issued through a public offering (in dollars per share)	$ 16.00	$ 12.00	$ 8.00
Gross proceeds from issuance	$ 100,000,000	$ 93,600,000	$ 82,800,000		$ 87,980,000	$ 77,521,000
Revenue Recognition
Number of types of licensing and development agreements with collaborative partners				2
Exclusive Licenses
Revenue Recognition
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				85,000	$ 1,300,000	$ 515,000
Number of types of milestone payments under collaborative arrangements				3
Exclusive Licenses | Minimum
Revenue Recognition
Period after product launch in which the company will earn royalty payments				10 years
T-DM1 royalty term on a country-by-country basis				10 years
Exclusive Licenses | Maximum
Revenue Recognition
Period after product launch in which the company will earn royalty payments				12 years
T-DM1 royalty term on a country-by-country basis				12 years
Right-to-Test Agreements | Minimum
Revenue Recognition
Average period over which upfront payments are deferred and recognized				12 months
Right-to-Test Agreements | Maximum
Revenue Recognition
Average period over which upfront payments are deferred and recognized				18 months
Amgen | Exclusive Licenses
Revenue Recognition
Number of single-target licenses				2
Bayer HealthCare | Exclusive Licenses
Revenue Recognition
Number of single-target licenses				1
Biotest | Exclusive Licenses
Revenue Recognition
Number of single-target licenses				1
Roche | Exclusive Licenses
Revenue Recognition
Number of single-target licenses				5