Nature of Business and Accounting Policies - Equity Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit	$ (858,669)	$ 1,852,978
Accounting standards update 2016-01, financial instruments | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit			$ 25,100