SUMMARY OF QUARTERLY DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
SUMMARY OF QUARTERLY DATA (UNAUDITED) [Abstract]
Revenues	$ 67,918	$ 59,670	$ 58,854	$ 58,258	$ 58,200	$ 52,772	$ 58,552	$ 57,696	$ 244,700	$ 227,220	$ 218,901
Gross profit	37,328	32,176	32,161	31,944	32,182	29,404	32,258	32,001	133,609	125,845	123,252
Income from continuing operations, net of tax	10,020	4,226	6,601	6,330	7,543	6,859	11,487	6,890	27,177	32,779	31,074
Gain (loss) from discontinued operations, net of tax	0	0	0	0	7	(15)	(55)	0	0	(63)	(3)
Net income	$ 10,020	$ 4,226	$ 6,601	$ 6,330	$ 7,550	$ 6,844	$ 11,432	$ 6,890	$ 27,177	$ 32,716	$ 31,630
Basic [Abstract]
Continuing operations (in dollars per share)	$ 0.44	$ 0.19	$ 0.29	$ 0.28	$ 0.33	$ 0.30	$ 0.51	$ 0.31	$ 1.20	$ 1.46	$ 1.37
Discontinued operations (in dollars per share)	0	0	0	0	0	0	0	0	0	(0.01)	0.03
Basic net income per share (in dollars per share)	0.44	0.19	0.29	0.28	0.33	0.30	0.51	0.31	1.20	1.45	1.40
Diluted [Abstract]
Continuing operations (in dollars per share)	0.43	0.18	0.29	0.28	0.33	0.30	0.51	0.30	1.17	1.44	1.36
Discontinued operations (in dollars per share)	0	0	0	0	0	0	(0.01)	0	0	0	0.02
Diluted net income per share (in dollars per share)	0.43	0.18	0.29	0.28	0.33	0.30	0.50	0.30	1.17	1.44	1.38
Cash dividends declared per share (in dollars per share)	$ 0.16	$ 0.16	$ 0.14	$ 0.14	$ 0.14	$ 0.14	$ 0.12	$ 0.12	$ 0.60	$ 0.52	$ 0.44