EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic EPS Calculation
Net income available for common stock	$ 20,623	$ 20,300	$ 97,079	$ 85,044
Weighted Average Number of Shares Outstanding, Basic	52,553	52,386	52,565	52,452
Earnings Per Share, Basic	$ 0.39	$ 0.39	$ 1.85	$ 1.62
Diluted EPS Calculation
Net income available for common stock	$ 20,623	$ 20,300	$ 97,079	$ 85,044
Effect of dilutive securities on income	$ 0	$ 0	$ 0	$ 0
Effect of dilutive securities on shares	416	450	447	520
Weighted Average Number of Shares Outstanding, Diluted	52,969	52,836	53,012	52,972
Earnings Per Share, Diluted	$ 0.39	$ 0.38	$ 1.83	$ 1.61