License agreement with Wyeth Holding Corporation (Details) (License agreement, Wyeth, USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended	90 Months Ended
	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2014
License agreement | Wyeth
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Notice period required for termination of license agreement		90 days
Aggregate amount of payments made under license agreement			$ 6.2
Sublicense payment made under license agreement	0.3
Expected milestone payment associated with the first Phase 3 clinical trial	$ 3.0	$ 3.0	$ 3.0