EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Antidilutive securities excluded from EPS calculation (in shares)	329,755		181,762		160,770	196,435
Net income (loss):
Net income	$ 41,022	$ (6,993)	$ 4,859	$ 13,870	$ 34,029	$ 18,729
Basic net income per common share (in dollars per share)	$ 1.99		$ 0.24		$ 1.65	$ 0.91
Diluted net income per common share (in dollars per share)	$ 1.99		$ 0.24		$ 1.65	$ 0.91
Weighted-average shares outstanding - basic (in shares)	20,618,000		20,488,000		20,588,000	20,471,000
Add: dilutive effect of contingent stock awards (in shares)	46,000		115,000		42,000	67,000
Weighted-average shares outstanding - diluted (in shares)	20,664,000		20,603,000		20,630,000	20,538,000