FOLOTYN License Agreement and Development Liability - Schedule of Drug Development Liability Adjustments (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Accrued Drug Development Expenses [Roll Forward]
Balance at December 31, 2017	$ 275
Balance at December 31, 2018	2,311
FOLOTYN [Member]
Accrued Drug Development Expenses [Roll Forward]
Balance at December 31, 2017	12,386
Transfer from long-term to current in 2018	0
(Less): Expenses incurred in 2018	(389)
Balance at December 31, 2018	11,997
FOLOTYN [Member] | FOLOTYN Development Liability, Current [Member]
Accrued Drug Development Expenses [Roll Forward]
Balance at December 31, 2017	275
Transfer from long-term to current in 2018	2,425
(Less): Expenses incurred in 2018	(389)
Balance at December 31, 2018	2,311
FOLOTYN [Member] | FOLOTYN Development Liability, Long Term [Member]
Accrued Drug Development Expenses [Roll Forward]
Balance at December 31, 2017	12,111
Transfer from long-term to current in 2018	(2,425)
(Less): Expenses incurred in 2018	0
Balance at December 31, 2018	$ 9,686