EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income (Numerator)
Income available to common stockholders (in dollars)	$ 43,391	$ 53,247	$ 57,539	$ 45,171	$ 41,598	$ 48,595	$ 53,076	$ 48,389	$ 199,348	$ 191,658	$ 171,994
Shares (Denominator)
Basic (in shares)	62,461	62,886	62,697	62,292	64,368	64,886	65,328	65,468	62,585	65,009	66,090
Total average equivalent shares	64,266	64,454	64,276	64,494	66,121	66,845	67,438	68,232	64,492	67,292	68,208
Per Share Amount
Net income per share, basic (in dollars per share)	$ 0.69	$ 0.85	$ 0.92	$ 0.73	$ 0.65	$ 0.75	$ 0.81	$ 0.74	$ 3.19	$ 2.95	$ 2.60
Net income per share, diluted (in dollars per share)	$ 0.68	$ 0.83	$ 0.90	$ 0.70	$ 0.63	$ 0.73	$ 0.79	$ 0.71	$ 3.09	$ 2.85	$ 2.52
Stock options
Shares (Denominator)
Effect of dilutive stock based compensation (in shares)									1,864	2,248	2,106
Restricted stock units
Shares (Denominator)
Effect of dilutive stock based compensation (in shares)									43	35	12