QUARTERLY DATA - UNAUDITED (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Mar. 31, 2020		Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2020		Mar. 31, 2019		Mar. 31, 2018
Condensed Quarterly Financial Information [Abstract]
Net sales	$ 366,476		$ 428,991		$ 411,565		$ 381,372		$ 325,434		$ 345,664		$ 345,043		$ 356,532		$ 1,588,404		$ 1,372,673		$ 1,418,802
Cost of Sales [Abstract]
Cost of sales	274,651		325,295		308,534		288,733		244,162		262,751		259,543		275,829		1,197,213		1,042,285		1,095,320
Gross profit	91,825		103,696		103,031		92,639		81,272		82,913		85,500		80,703		391,191		330,388		323,482
Selling, general, and administrative expenses	69,782		73,090		70,523		65,787		62,683		59,728		57,705		56,966		279,182		237,082		228,127
Depreciation and amortization	3,489		3,647		3,557		3,463		3,574		2,719		2,741		2,790		14,156		11,824		9,921
Interest and financing costs	676		694		576		628		545		443		484		476		2,574		1,948		1,195
Operating expenses	73,947		77,431		74,656		69,878		66,802		62,890		60,930		60,232		295,912		250,854		239,243
Operating income	17,878		26,265		28,375		22,761		14,470		20,023		24,570		20,471		95,279		79,534		84,239
Other income and (expense)	(232)		997		(40)		(45)		5,556		721		322		97		680		6,696		(348)
Earnings before tax	17,646		27,262		28,335		22,716		20,026		20,744		24,892		20,568		95,959		86,230		83,891
Provision for income taxes	4,400		7,712		8,237		6,528		4,974		5,880		6,889		5,295		26,877		23,038		28,769
Net earnings	$ 13,246		$ 19,550		$ 20,098		$ 16,188		$ 15,052		$ 14,864		$ 18,003		$ 15,273		$ 69,082		$ 63,192		$ 55,122
Net earnings per common share - Basic (in dollars per share)	$ 0.99	[1]	$ 1.47	[1]	$ 1.51	[1]	$ 1.21	[1]	$ 1.12	[1]	$ 1.10	[1]	$ 1.33	[1]	$ 1.14	[1]	$ 5.18	[1]	$ 4.70	[1]	$ 4.00
Net earnings per common share - Diluted (in dollars per share)	$ 0.99	[1]	$ 1.46	[1]	$ 1.51	[1]	$ 1.20	[1]	$ 1.12	[1]	$ 1.10	[1]	$ 1.33	[1]	$ 1.12	[1]	$ 5.15	[1]	$ 4.65	[1]	$ 3.95
Product [Member]
Condensed Quarterly Financial Information [Abstract]
Net sales	$ 317,621		$ 378,569		$ 363,497		$ 335,601		$ 280,460		$ 310,443		$ 309,475		$ 322,817		$ 1,395,288		$ 1,223,195		$ 1,289,307
Cost of Sales [Abstract]
Cost of sales	244,638		293,209		278,863		260,063		216,662		241,856		238,134		255,812		1,076,773		952,464		1,023,590
Service [Member]
Condensed Quarterly Financial Information [Abstract]
Net sales	48,855		50,422		48,068		45,771		44,974		35,221		35,568		33,715		193,116		149,478		129,495
Cost of Sales [Abstract]
Cost of sales	$ 30,013		$ 32,086		$ 29,671		$ 28,670		$ 27,500		$ 20,895		$ 21,409		$ 20,017		$ 120,440		$ 89,821		$ 71,730

[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.