Restatement of Previously Issued Financial Statements - Balance Sheets and Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Feb. 28, 2017	Nov. 30, 2016	Aug. 31, 2016	May 31, 2016	Feb. 29, 2016	Nov. 30, 2015	Aug. 31, 2015	May 31, 2015	Feb. 28, 2017	Feb. 29, 2016	Feb. 28, 2015	Feb. 28, 2014
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Inventories - net	$ 94,007				$ 77,131				$ 94,007	$ 77,131
Costs and estimated earnings in excess of billings on uncompleted contracts	50,262				63,482				50,262	63,482
Total current assets	297,052				315,525				297,052	315,525
Assets	978,354				988,201				978,354	988,201	$ 925,315
Other accrued liabilities	24,042				26,137				24,042	26,137
Customer advance payment	1,459				0				1,459	0
Billings in excess of costs and estimated earnings on uncompleted contracts	20,617				20,302				20,617	20,302
Total Current Liabilities	136,770				149,549				136,770	149,549
Deferred income tax liabilities	53,648				51,853				53,648	51,853
Total liabilities	445,218				503,831				445,218	503,831
Retained earnings	498,527				453,908				498,527	453,908
Total Shareholders’ Equity	533,136				484,370				533,136	484,370	424,452	$ 379,640
Total Liabilities and Shareholders’ Equity	978,354				988,201				978,354	988,201
Net Income	12,270	$ 16,646	$ 10,159	$ 22,189	15,182	$ 22,822	$ 14,866	$ 22,674	61,264	75,544	65,616
Deferred income tax expense									1,714	1,960	16,222
Inventories									(13,754)	(2,052)	(3,363)
Net change in billings related to costs and estimated earnings on uncompleted contracts									13,592	7,276	(13,823)
Other accrued liabilities and income taxes payable									(10,211)	9,755	(5,865)
Net cash provided by operating activities:									111,176	143,589	118,157
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Inventories - net	123,208				102,135				123,208	102,135
Costs and estimated earnings in excess of billings on uncompleted contracts	20,546				32,287				20,546	32,287
Total current assets	296,537				309,334				296,537	309,334
Assets	977,839				982,010				977,839	982,010
Other accrued liabilities	18,390				20,406				18,390	20,406
Customer advance payment	20,860				15,652				20,860	15,652
Billings in excess of costs and estimated earnings on uncompleted contracts	11,948				9,237				11,948	9,237
Total Current Liabilities	141,850				148,405				141,850	148,405
Deferred income tax liabilities	51,550				49,960				51,550	49,960
Total liabilities	448,200				500,794				448,200	500,794
Retained earnings	495,030				450,754				495,030	450,754
Total Shareholders’ Equity	529,639				481,216				529,639	481,216	420,052	375,913
Total Liabilities and Shareholders’ Equity	977,839				982,010				977,839	982,010
Net Income	11,584	18,251	10,023	21,063	16,076	23,547	17,243	19,924	60,921	76,790	64,943
Deferred income tax expense									1,509	2,707	15,818
Inventories									(17,951)	11,124	(879)
Net change in billings related to costs and estimated earnings on uncompleted contracts									14,509	5,739	(5,635)
Other accrued liabilities and income taxes payable									(6,383)	(3,877)	(15,460)
Net cash provided by operating activities:									111,176	143,589	118,157
Correction
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Inventories - net	(29,201)				(25,004)				(29,201)	(25,004)
Costs and estimated earnings in excess of billings on uncompleted contracts	29,716				31,195				29,716	31,195
Total current assets	515				6,191				515	6,191
Assets	515				6,191				515	6,191
Other accrued liabilities	5,652				5,731				5,652	5,731
Customer advance payment	(19,401)				(15,652)				(19,401)	(15,652)
Billings in excess of costs and estimated earnings on uncompleted contracts	8,669				11,065				8,669	11,065
Total Current Liabilities	(5,080)				1,144				(5,080)	1,144
Deferred income tax liabilities	2,098				1,893				2,098	1,893
Total liabilities	(2,982)				3,037				(2,982)	3,037
Retained earnings	3,497				3,154				3,497	3,154
Total Shareholders’ Equity	3,497				3,154				3,497	3,154	4,400	$ 3,727
Total Liabilities and Shareholders’ Equity	515				6,191				515	6,191
Net Income	$ 686	$ (1,605)	$ 136	$ 1,126	$ (894)	$ (725)	$ (2,377)	$ 2,750	343	(1,246)	673
Deferred income tax expense									205	(747)	404
Inventories									4,197	(13,176)	(2,484)
Net change in billings related to costs and estimated earnings on uncompleted contracts									(917)	1,537	(8,188)
Other accrued liabilities and income taxes payable									(3,828)	13,632	9,595
Net cash provided by operating activities:									$ 0	$ 0	$ 0