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Intangible Assets and Goodwill - Intangible Assets, Net (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Intangible assets
Finite-lived intangible assets		$ 0	$ 7,100
Non-cash impairment charge, indefinite-lived			13,000
Indefinite-lived intangible assets		48,700	60,500
Amortization of Acquired Intangible Assets		$ 224	$ 896	$ 997
IPR&D
Intangible assets
Non-cash impairment charge, indefinite-lived	$ 11,800
License Rights
Intangible assets
Non-cash impairment charge, finite lived	$ 6,900