STOCKHOLDERS' EQUITY - GSR Agreement (Details) $ in Thousands	May 08, 2019 USD ($) shares	May 06, 2019 USD ($)	Aug. 09, 2018 $ / token	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Class of Stock [Line Items]
Post-money valuation				$ 5,088	$ 5,855
GSR Capital
Class of Stock [Line Items]
Sale of tokens (in usd per token) | $ / token			6.67
tZero.com, Inc. | Subsequent Event
Class of Stock [Line Items]
Number of shares sold in transaction (in shares) | shares	508,710
Number of shares sold in transaction as percentage of total shares issued and outstanding	0.50%
Total consideration received from sale of stock	$ 5,000
Consideration received from sale of stock	1,000
Value of shares received from sale of stock	$ 3,000
tZero.com, Inc. | GSR Capital | Subsequent Event
Class of Stock [Line Items]
Cash portion of acquisition price		$ 30,000