EARNINGS PER SHARE - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator for basic and diluted earnings per share:
Net income	$ 36,369	$ 36,244	$ 976	$ 31,089	$ 30,747	$ (12,631)	$ 73,589	$ 49,205
Denominator:
Basic shares outstanding (in shares)	55,850			56,059			55,858	56,222
Dilutive effect of outstanding stock awards (in shares)	315			232			251	138
Dilutive shares outstanding (in shares)	56,165			56,291			56,109	56,360
Basic income (in USD per share)	$ 0.65			$ 0.55			$ 1.32	$ 0.88
Diluted income (in USD per share)	$ 0.65			$ 0.55			$ 1.31	$ 0.87