Intangible assets (Details) (USD $)	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Amortized intangible assets [Abstract]
Gross carrying amount	$ 2,450,328,000	$ 2,326,738,000
Accumulated amortization	322,689,000	222,690,000
Amortization expense	99,900,000	80,900,000	30,800,000
Finite-Lived Intangible Assets, Future Amortization Expense [Abstract]
2014	135,362,000
2015	210,118,000
2016	238,809,000
2017	284,804,000
2018	335,950,000
Future expected amortization expense	1,205,043,000
Licensing Agreements [Member]
Amortized intangible assets [Abstract]
Gross carrying amount	1,528,114,000	1,403,114,000
Accumulated amortization	160,805,000	107,314,000
Product Rights [Member]
Amortized intangible assets [Abstract]
Gross carrying amount	89,407,000	90,817,000
Accumulated amortization	61,472,000	52,929,000
Buy-out of royalty agreements [Member]
Amortized intangible assets [Abstract]
Gross carrying amount	798,617,000	798,617,000
Accumulated amortization	66,222,000	28,257,000
Trade Names [Member]
Amortized intangible assets [Abstract]
Gross carrying amount	34,190,000	34,190,000
Accumulated amortization	$ 34,190,000	$ 34,190,000