Collaborative and Other Relationships Collaborative and Other Relationships - Collaborations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development	$ 519,863	$ 417,174	$ 1,471,140	$ 1,393,331
Mitsubishi Tanabe Pharma Corporation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development	60,000
Potential future milestone payments	484,000		484,000
AGTC
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development	56,800
Potential future milestone payments	1,000,000		1,000,000
Upfront milestone payment	124,000
Purchase of common stock	30,000
Prepaid research and development	58,400		58,400
Total licensing and fees	35,600
Research and development services	8,700
Premium on equity investment	7,500
Swedish Orphan Biovitrum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional milestone payment	10,000		10,000
Lead programs | AGTC
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development	5,000
Potential future milestone payments	472,500		472,500
Discovery programs | AGTC
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future milestone payments	$ 592,500		$ 592,500