EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net income (loss)	$ 70,539	$ 106,126	$ 200,227	$ 223,322
Denominator (shares in 000's):
Basic weighted average shares outstanding (in shares)	64,821,000	65,806,000	65,245,000	65,769,000
Effect of dilutive securities - Stock options and awards (in shares)	831,000	896,000	810,000	910,000
Diluted weighted average shares outstanding (in shares)	65,652,000	66,702,000	66,055,000	66,679,000
Earnings (loss) per share
Basic earnings (loss) per share (in dollars per share)	$ 1.09	$ 1.61	$ 3.07	$ 3.40
Diluted earnings (loss) per share (in dollars per share)	$ 1.07	$ 1.59	$ 3.03	$ 3.35
Anti-dilutive shares excluded from the computation of diluted earnings per share	346,168	182,615	317,528	807,763