Business Combination - Purchase Price Allocation (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill		$ 13,064	$ 16,864
Adjustment
Adjustment		14,600	0	$ 0
Viventia Bio Inc.
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Cash and cash equivalents		136	136
Prepaid expenses and other assets		1,162	1,162
Property and equipment		867	867
In-process research and development assets (all markets)		46,400	60,500
Goodwill		13,064	16,864
Accounts payable		(1,163)	(1,163)
Accrued expenses		(2,001)	(1,494)
Other liabilities		(812)	(812)
Deferred tax liability		(12,528)	(16,335)
Recognized assets acquired, goodwill, and liabilities assumed, net		$ 45,125	$ 59,725
Adjustment
Cash and cash equivalents	$ 0
Prepaid expenses and other assets	0
Property and equipment	0
In-process research and development assets (all markets)	(14,100)
Goodwill	(3,800)
Accounts payable	0
Accrued expenses	(507)
Other liabilities	0
Deferred tax liability	3,807
Adjustment	$ 14,600