EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2014		Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Weighted average number diluted shares outstanding adjustment [Abstract]
Restricted stock awards that contain non-forfeitable rights to dividends (in shares)																	0	0
Calculation of earnings per common share - basic [Abstract]
Net earnings	$ 10,490		$ 12,620		$ 16,775		$ 10,671		$ 9,957		$ 10,297		$ 15,679		$ 8,814		$ 50,556	$ 44,747	$ 45,840
Net earnings attributable to participating securities																	0	0	59
Net earnings attributable to common share holders																	50,556	44,747	45,781
Calculation of earnings per common share - diluted [Abstract]
Net earnings attributable to common shareholders- basic																	50,556	44,747	45,781
Add: undistributed earnings attributable to participating securities																	0	0	1
Net earnings attributable to common shareholders- diluted																	$ 50,556	$ 44,747	$ 45,782
Basic and diluted common shares outstanding [Abstract]
Weighted average common shares outstanding - basic (in shares)																	13,867,000	14,513,000	14,636,000
Effect of dilutive shares (in shares)																	161,000	175,000	150,000
Weighted average shares common outstanding-diluted (in shares)																	14,028,000	14,688,000	14,786,000
Earnings per common share - basic (in dollars per share)	$ 0.76	[1]	$ 0.92	[1]	$ 1.21	[1]	$ 0.76	[1]	$ 0.69	[1]	$ 0.71	[1]	$ 1.08	[1]	$ 0.61	[1]	$ 3.65	$ 3.08	$ 3.13
Earnings per common share - diluted (in dollars per share)	$ 0.75	[1]	$ 0.91	[1]	$ 1.21	[1]	$ 0.75	[1]	$ 0.68	[1]	$ 0.70	[1]	$ 1.07	[1]	$ 0.60	[1]	$ 3.60	$ 3.05	$ 3.10
Unexercised stock options (in shares)	0								0								0	0	0

[1] Basic and diluted earnings per share are computed independently for each of the quarters presented. Therefore, the sum of quarterly basic and diluted per share information may not equal annual basic and diluted earnings per share.