EQUITY CAPITALIZATION (Details) $ / shares in Units, $ in Thousands						12 Months Ended
	Nov. 09, 2017 $ / shares shares	Mar. 28, 2017 executive director shares	Mar. 22, 2017 USD ($) $ / shares shares	Dec. 27, 2016 USD ($) $ / shares shares	Jun. 08, 2016 USD ($) shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($)	Sep. 30, 2013 $ / shares
Subsidiary, Sale of Stock [Line Items]
Proceeds from additional common equity capitalization | $						$ 0	$ 40,425	$ 0
Proceeds from preferred equity capitalization | $				$ 170,000		$ 0	$ 170,000	0
Preferred stock, par value (in dollars per share) | $ / shares						$ 0.001	$ 0.001
Payment of IPO costs | $						$ 0	$ 7,489	0
Preferred stock, issued (in shares)						0	16,999,990
Preferred stock, outstanding (in shares)						0	16,999,990
Common stock, par value (in dollars per share) | $ / shares						$ 0.001	$ 0.001		$ 0.001
Proceeds from IPO | $						$ 185,500	$ 0	0
Repayment of outstanding borrowings | $			$ 71,800			166,546	41,295	73,782
Capital expenditures | $			$ 86,800			$ 285,891	$ 42,832	$ 62,855
Number of executives | executive		1
Number of directors | director		1
Exercisable (in shares)		226,194
Exercised (in shares)		162,212				226,194
Common stock, outstanding (in shares)						83,039,854	52,627,652
Private Placement
Subsidiary, Sale of Stock [Line Items]
Shares of common stock sold, including shares sold by third parties (in shares)				16,999,990
Preferred stock, par value (in dollars per share) | $ / shares				$ 0.001
Payment of IPO costs | $				$ 7,000
Preferred equity capitalization, net of costs | $				$ 163,000
IPO
Subsidiary, Sale of Stock [Line Items]
Shares of common stock sold, including shares sold by third parties (in shares)			25,000,000
Common stock, par value (in dollars per share) | $ / shares			$ 0.001
Stock price (in dollars per share) | $ / shares			$ 14.00
Proceeds from IPO | $			$ 170,100
Payment of underwriting discounts and commissions | $			10,900
Payments of stock issuance costs, other | $			$ 4,500
IPO Sold By Company
Subsidiary, Sale of Stock [Line Items]
Shares of common stock sold, including shares sold by third parties (in shares)			13,250,000
IPO sold by existing stockholders
Subsidiary, Sale of Stock [Line Items]
Shares of common stock sold, including shares sold by third parties (in shares)			11,750,000
Series A convertible preferred stock
Subsidiary, Sale of Stock [Line Items]
Preferred stock, issued (in shares)							16,999,990
Performance stock units | IPO
Subsidiary, Sale of Stock [Line Items]
Number of shares of outstanding stock converted (in shares)			16,999,990
Series A Preferred Stock Converted To Common Stock | IPO
Subsidiary, Sale of Stock [Line Items]
Shares of common stock issued for each share of preferred stock converted			1
Energy Capital Partners Affiliates
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock (in shares)	13,800,000
Shares issued, price per share (in dollars per share) | $ / shares	$ 15.07
Energy Capital Partners Affiliates
Subsidiary, Sale of Stock [Line Items]
Proceeds from additional common equity capitalization | $					$ 40,400
Issuance of common stock (in shares)					18,007,328