NET EARNINGS PER COMMON SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings (Numerator) [Abstract]
Basic EPS - Net earnings									$ 90,071	$ 55,972	$ 59,722
Diluted EPS - Net earnings									$ 90,071	$ 55,972	$ 59,722
Number of Shares (Denominator) [Abstract]
Basic EPS - weighted average common shares outstanding (in shares)									31,838,641	31,521,667	31,158,142
Effect of dilutive securities - stock options, restricted stock, and performance shares (in shares)									391,165	400,971	477,496
Diluted EPS - stock options, restricted stock, and performance shares (in shares)									32,229,806	31,922,638	31,635,638
Per Share Amount [Abstract]
Basic EPS - Net earnings (in dollars per share)	$ 1.31	$ 0.50	$ 0.52	$ 0.49	$ 0.51	$ 0.44	$ 0.45	$ 0.38	$ 2.83	$ 1.78	$ 1.92
Diluted EPS - Net earnings (in dollars per share)	$ 1.30	$ 0.50	$ 0.51	$ 0.48	$ 0.50	$ 0.44	$ 0.44	$ 0.37	$ 2.79	$ 1.75	$ 1.89
Stock Options [Member]
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)									199,010	2,500	194,372