EARNINGS PER SHARE - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Numerator for basic and diluted earnings per share:
Net income	$ 36,244	$ 976	$ 30,747	$ (12,631)	$ 37,220	$ 18,116
Denominator:
Basic shares outstanding (in shares)	55,875		56,410		55,861	56,304
Dilutive effect of stock-based compensation awards (in shares)	191		95		140	95
Dilutive shares outstanding (in shares)	56,066		56,505		56,001	56,399
Basic income (in USD per share)	$ 0.65		$ 0.55		$ 0.67	$ 0.32
Diluted income (in USD per share)	$ 0.65		$ 0.54		$ 0.66	$ 0.32