STOCKHOLDERS' EQUITY - Narrative (Details)			6 Months Ended	12 Months Ended
	Feb. 01, 2018 USD ($) shares	Jan. 24, 2017 USD ($) shares	Jun. 30, 2017 class	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Apr. 07, 2016 shares	Jan. 12, 2016 USD ($)	Jul. 28, 2015 USD ($)
Class of Stock [Line Items]
Number of classes of stock | class			2
Preferred stock, shares authorized (in shares)				5,000,000	5,000,000
Preferred stock, par value (in dollars per share) | $ / shares				$ 0.001	$ 0.001
Common stock, shares authorized (in shares)				50,000,000	50,000,000
Common stock, par value (in dollars per share) | $ / shares				$ 0.001	$ 0.001
Authorized amount of shares to be repurchased | $							$ 70,000,000.0	$ 15,000,000.0
Repurchase of common stock (in shares)				0	0
Remaining authorized repurchase amount | $				$ 32,000,000.0
Restricted Stock
Class of Stock [Line Items]
Stock-based compensation expense recognized | $				$ 0	$ 35,000
2016 Plan | Restricted Stock
Class of Stock [Line Items]
Number of shares granted (in shares)	34,202	56,260		34,202	56,260
Shares vesting period	3 years	3 years
Value of shares granted | $	$ 554,000	$ 1,400,000
Common Stock | 2016 Plan
Class of Stock [Line Items]
Number of shares authorized (in shares)						2,500,000
Number of shares available for issuance (in shares)				2,359,671