Summary of Significant Accounting Policies - Going Concern and Management's Plans (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019
Debt Instrument [Line Items]
Cash and cash equivalents	$ 80,752				$ 106,999				$ 80,752	$ 106,999
Accumulated deficit	758,644				686,016				758,644	686,016
Net loss	16,648	$ 14,039	$ 13,884	$ 28,057	$ 9,046	$ 34,296	$ 33,835	$ 51,888	72,628	$ 129,065
Gross interest bearing indebtedness	15,700								15,700
Other non-interest bearing current liabilities	$ 16,600								$ 16,600