NET EARNINGS PER COMMON SHARE (Details) - USD ($) $ / shares in Units, $ 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
Earnings (Numerator) [Abstract]
Basic EPS - Net earnings									$ 78,573	$ 90,071	$ 55,972
Diluted EPS - Net earnings									$ 78,573	$ 90,071	$ 55,972
Number of Shares (Denominator) [Abstract]
Basic EPS - weighted average common shares outstanding (in shares)									32,093,037	31,838,641	31,521,667
Effect of dilutive securities - stock options, restricted stock, and performance shares (in shares)									351,858	391,165	400,971
Diluted EPS - weighted average common shares outstanding and effect of stock options, restricted stock and performance shares (in shares)									32,444,895	32,229,806	31,922,638
Per Share Amount [Abstract]
Basic EPS - Net earnings (in dollars per share)	$ 0.63	$ 0.60	$ 0.61	$ 0.60	$ 1.31	$ 0.50	$ 0.52	$ 0.49	$ 2.45	$ 2.83	$ 1.78
Diluted net earnings per common share (in dollars per share)	$ 0.63	$ 0.59	$ 0.61	$ 0.60	$ 1.30	$ 0.50	$ 0.51	$ 0.48	$ 2.42	$ 2.79	$ 1.75
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive stock options outstanding, excluded from diluted earnings per share calculation (in shares)									188,470	199,010	2,500