EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earning per share
Authorized common stock (in shares)	199,000				199,000				199,000	199,000
Common stock, par value (in dollars per share)	$ 0.01				$ 0.01				$ 0.01	$ 0.01
Income (Numerator)
Income available to common stockholders, basic (in dollars)	$ 40,674	$ 38,996	$ 55,775	$ 59,300	$ 49,513	$ 53,523	$ 65,174	$ 51,820	$ 194,745	$ 220,030	$ 205,590
Income available to common stockholders, diluted (in dollars)									$ 194,745	$ 220,030	$ 205,590
Shares (Denominator)
Basic (in shares)	62,834	62,378	62,402	62,128	61,944	62,592	62,631	62,355	62,437	62,435	62,804
Total average equivalent shares	65,344	65,129	64,850	64,414	64,528	64,821	64,828	64,234	64,958	64,596	64,849
Per Share Amount
Net income per share, basic (in dollars per share)	$ 0.65	$ 0.63	$ 0.89	$ 0.95	$ 0.80	$ 0.86	$ 1.04	$ 0.83	$ 3.12	$ 3.52	$ 3.27
Net income per share, diluted (in dollars per share)	$ 0.62	$ 0.60	$ 0.86	$ 0.92	$ 0.77	$ 0.83	$ 1.01	$ 0.81	$ 3.00	$ 3.41	$ 3.17
Stock options
Shares (Denominator)
Effect of dilutive stock based compensation (in shares)									2,440	2,106	1,988
Restricted stock units
Shares (Denominator)
Effect of dilutive stock based compensation (in shares)									81	55	57