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Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jan. 01, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Product Information [Line Items]
Cumulative adjustment to retained earnings							$ 1	$ 1,573
Gross product sales		$ 36,659	$ 17,277	$ 68,261	$ 28,844
Product sales allowances		39,625		39,625		$ 25,503
Cost of product sales		$ 13,588	$ 5,231	$ 28,550	$ 8,364
Accounting Standards Update 2014-09
Product Information [Line Items]
Gross product sales	$ 2,900
Cost of product sales	200
Accounting Standards Update 2014-09 \| Product Sales Allowance
Product Information [Line Items]
Product sales allowances	1,100
Retained Earnings
Product Information [Line Items]
Cumulative adjustment to retained earnings							$ 1	$ 1,573
Retained Earnings \| Accounting Standards Update 2014-09
Product Information [Line Items]
Cumulative adjustment to retained earnings	$ 1,600