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Investments - Additional Information (Details) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Investment [Line Items]      
Realized (loss) gain on trading securities $ 1,800,000 $ (1,500,000) $ (300,000)
Distributions from equity method investments $ 4,178,000 $ 911,000 0
Capital contributions to equity method investments     2,500,000
Capital commitments      
Investment [Line Items]      
Future capital commitment (up to)     $ 700,000