EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income (Numerator)
Income available to common stockholders (in dollars)	$ 49,581	$ 53,098	$ 59,048	$ 43,863	$ 43,391	$ 53,247	$ 57,539	$ 45,171	$ 205,590	$ 199,348	$ 191,658
Shares (Denominator)
Basic (in shares)	62,586	62,858	63,053	62,722	62,461	62,886	62,697	62,292	62,804	62,585	65,009
Total average equivalent shares	64,220	64,690	64,785	65,063	64,266	64,454	64,276	64,494	64,849	64,492	67,292
Per Share Amount
Net income per share, basic (in dollars per share)	$ 0.79	$ 0.84	$ 0.94	$ 0.70	$ 0.69	$ 0.85	$ 0.92	$ 0.73	$ 3.27	$ 3.19	$ 2.95
Net income per share, diluted (in dollars per share)	$ 0.77	$ 0.82	$ 0.91	$ 0.67	$ 0.68	$ 0.83	$ 0.90	$ 0.70	$ 3.17	$ 3.09	$ 2.85
Stock options
Shares (Denominator)
Effect of dilutive stock based compensation (in shares)									1,988	1,864	2,248
Restricted stock units
Shares (Denominator)
Effect of dilutive stock based compensation (in shares)									57	43	35