Condensed Consolidated Balance Sheets (Parentheticals) - $ / shares
Jun. 30, 2019
Apr. 02, 2019
Dec. 31, 2018
Preferred stock, par value (in dollars per share) $ 0.0001   $ 0.0001
Preferred stock, shares authorized 50,000,000   50,000,000
Preferred stock, shares issued 0   0
Preferred stock, shares outstanding 0   0
Class A common stock      
Common stock, par value $ 0.0001 $ 0.0001 $ 0.0001
Common stock, shares authorized 150,000,000   150,000,000
Common stock, shares issued 114,021,830   91,859,638
Common stock, shares outstanding 114,021,830   91,859,638
Class B common stock      
Common stock, par value $ 0.0001   $ 0.0001
Common stock, shares authorized 50,000,000   50,000,000
Common stock, shares issued 0   0
Common stock, shares outstanding 0   0