Consolidated balance sheets (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	45,000,000	45,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Class A Common Stock [Member]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	513,797,000	513,797,000
Common stock, shares issued	39,672,000	38,349,000
Common stock, shares outstanding	39,672,000	38,349,000
Class B Common Stock [Member]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	41,203,000	41,203,000
Common stock, shares issued	31,901,000	32,171,000
Common stock, shares outstanding	31,901,000	32,171,000