CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, authorized	15,000,000	15,000,000
Preferred stock, issued	0	0
Preferred stock, outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, authorized	250,000,000	250,000,000
Common stock, issued	47,671,446	37,341,393
Common stock, outstanding	47,671,446	37,341,393
Cash and cash equivalents	$ 13,546	$ 17,080
Prepaid expenses and other current assets	1,194	743
Accounts payable and accrued expenses	10,706	9,122
Variable Interest Entity [Member]
Cash and cash equivalents	12,220	13,175
Prepaid expenses and other current assets	610	273
Accounts payable and accrued expenses	$ 148	$ 0