BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - NATURE OF BUSINESS (Details) $ / shares in Units, $ in Thousands			12 Months Ended
	Jul. 17, 2015 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) $ / shares shares	Dec. 31, 2017 segment item	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) shares
NATURE OF BUSINESS
Number of tankers | item			30
Number of reporting segments | segment			1
Issuance of common stock for initial public offering (in shares) | shares					15,000,000
Gross proceeds from issuance of common stock				$ 26	$ 236,351
Issuance cost					$ 6,543
IPO
NATURE OF BUSINESS
Issuance of common stock for initial public offering (in shares) | shares		15,000,000
Share price (in dollars per share) | $ / shares		$ 14.00
Gross proceeds from IPO		$ 210,000
Net proceeds from issuance of common stock		$ 196,400
Over-allotment option
NATURE OF BUSINESS
Issuance of common stock for initial public offering (in shares) | shares	1,882,223
Share price (in dollars per share) | $ / shares	$ 14.00
Gross proceeds from issuance of common stock	$ 26,400
Net proceeds from issuance of common stock	$ 24,600
VLCCs
NATURE OF BUSINESS
Number of vessels including those remained on time charter | item			21
Suezmax tankers
NATURE OF BUSINESS
Number of tankers | item			6
Aframax
NATURE OF BUSINESS
Number of tankers | item			1
Panamax tankers
NATURE OF BUSINESS
Number of tankers | item			2