EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net income (loss)	$ 68,864	$ 61,352	$ 129,688	$ 117,196
Denominator (shares in 000's):
Basic weighted average shares outstanding (in shares)	65,337,000	65,811,000	65,458,000	65,750,000
Effect of dilutive securities - Stock options and awards (in shares)	784,000	932,000	799,000	916,000
Diluted weighted average shares outstanding (in shares)	66,121,000	66,743,000	66,257,000	66,666,000
Earnings (loss) per share
Basic earnings (loss) per share (in dollars per share)	$ 1.05	$ 0.93	$ 1.98	$ 1.78
Diluted earnings (loss) per share (in dollars per share)	$ 1.04	$ 0.92	$ 1.96	$ 1.76
Anti-dilutive shares excluded from the computation of diluted earnings per share	346,168	179,178	303,207	133,748