License Agreement with Wyeth Holdings LLC (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Increase in accrued milestone payment	$ 4.0
Minimum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Increase in accrued milestone payment	3.0
License agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate amount of payments made under license agreement	$ 11.6