CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ 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	Jun. 30, 2015	[1]	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
CONSOLIDATED STATEMENTS OF OPERATIONS [Abstract]
Net sales	$ 330,426		$ 342,569		$ 370,845		$ 367,157		$ 332,767		$ 326,657		$ 371,462		$ 298,503			$ 1,410,997	$ 1,329,389	$ 1,204,199
Cost of sales	248,796		265,881		283,274		289,564		256,391		252,871		289,529		230,839			1,087,515	1,029,630	942,142
Gross profit	81,630		76,688		87,571		77,593		76,376		73,786		81,933		67,664			323,482	299,759	262,057
Selling, general, and administrative expenses	59,989		57,134		56,340		54,664		55,411		50,160		51,607		48,054			228,127	205,232	178,980
Depreciation and amortization	2,835		2,894		2,129		2,063		1,844		1,910		1,723		1,775			9,921	7,252	5,548
Interest and financing costs	292		270		274		359		385		409		400		349			1,195	1,543	1,778
Operating expenses	63,116		60,298		58,743		57,086		57,640		52,479		53,730		50,178			239,243	214,027	186,306
Operating income	18,514		16,390		28,828		20,507		18,736		21,307		28,203		17,486			84,239	85,732	75,751
Other income (expense)	(347)		(131)		(141)		271		0		0		380		0			(348)	380	0
Earnings before tax	18,167		16,259		28,687		20,778		18,736		21,307		28,583		17,486			83,891	86,112	75,751
Provision for income taxes	9,270		678		11,466		7,355		8,246		8,687		11,808		6,815			28,769	35,556	31,004
Net earnings	$ 8,897		$ 15,581		$ 17,221		$ 13,423		$ 10,490		$ 12,620		$ 16,775		$ 10,671			$ 55,122	$ 50,556	$ 44,747
Net earnings per common share-basic (in dollars per share)	$ 0.65	[1]	$ 1.12	[1]	$ 1.24	[1]	$ 0.97	[1]	$ 0.76	[1]	$ 0.92	[1]	$ 1.21	[1]		$ 0.76		$ 4.00	$ 3.65	$ 3.08
Net earnings per common share-diluted (in dollars per share)	$ 0.65	[1]	$ 1.11	[1]	$ 1.23	[1]	$ 0.96	[1]	$ 0.75	[1]	$ 0.91	[1]	$ 1.21	[1]		$ 0.75		$ 3.95	$ 3.60	$ 3.05
Weighted average common shares outstanding-basic (in shares)																		13,790	13,867	14,513
Weighted average common shares outstanding-diluted (in shares)																		13,967	14,028	14,688

[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.