REVENUES - Reconciliation of ASC 606 to Prior Standards (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2018
Consolidated Balance Sheets
Contract assets	$ 99,499		$ 99,499		$ 53,034
Inventories	126,816		126,816		135,416
Total current assets	450,206		450,206		396,023
Total assets	1,326,095		1,326,095		1,265,122
Contract liabilities	53,758		53,758		49,035
Total current liabilities	199,736		199,736		200,530
Deferred tax liabilities	66,286		66,286
Total liabilities	514,288		514,288		505,712
Retained earnings	661,003		661,003		606,837
Total shareholders' equity	811,807	$ 727,254	811,807	$ 727,254	759,410
Total liabilities and shareholders' equity	1,326,095		1,326,095		$ 1,265,122
Consolidated Statements of Operations
Net sales	199,766	192,223	576,312	540,496
Cost of sales	122,172	122,805	363,026	346,911
Total costs and expenses	174,874	168,907	506,808	490,795
Earnings before income tax	24,892	23,316	69,504	49,701
Income tax expense (benefit)	4,825	4,297	13,323	(13,983)
Net earnings	$ 20,067	$ 19,019	$ 56,181	$ 63,684
Basic:
Net earnings	$ 0.77	$ 0.73	$ 2.17	$ 2.46
Diluted:
Net earnings	$ 0.77	$ 0.73	$ 2.15	$ 2.45
Consolidated Statements of Comprehensive Income
Net earnings	$ 20,067	$ 19,019	$ 56,181	$ 63,684
Comprehensive income	21,899	12,092	54,262	61,037
Consolidated Statements of Cash flows
Net earnings	20,067	$ 19,019	56,181	63,684
Adjustments to reconcile net earnings to net cash provided by operating activities:
Change in assets and liabilities			(41,851)	(9,454)
Net cash provided by operating activities			37,041	$ 53,944
Effect of the Effect of ASU 606
Consolidated Balance Sheets
Contract assets	(43,576)		(43,576)
Inventories	36,089		36,089
Total current assets	(7,487)		(7,487)
Total assets	(7,487)		(7,487)
Contract liabilities	4,549		4,549
Total current liabilities	4,549		4,549
Deferred tax liabilities	(1,678)		(1,678)
Total liabilities	2,871		2,871
Retained earnings	(10,358)		(10,358)
Total shareholders' equity	(10,358)		(10,358)
Total liabilities and shareholders' equity	(7,487)		(7,487)
Consolidated Statements of Operations
Net sales	(4,008)		(9,787)
Cost of sales	(1,380)		(8,360)
Total costs and expenses	(1,380)		(8,360)
Earnings before income tax	(2,628)		(1,427)
Income tax expense (benefit)	(399)		(171)
Net earnings	$ (2,229)		$ (1,256)
Basic:
Net earnings	$ (0.08)		$ (0.05)
Diluted:
Net earnings	$ (0.08)		$ (0.04)
Consolidated Statements of Comprehensive Income
Net earnings	$ (2,229)		$ (1,256)
Comprehensive income	(2,229)		(1,256)
Consolidated Statements of Cash flows
Net earnings	(2,229)		(1,256)
Adjustments to reconcile net earnings to net cash provided by operating activities:
Change in assets and liabilities			1,256
Under Prior Accounting
Consolidated Balance Sheets
Contract assets	55,923		55,923
Inventories	162,905		162,905
Total current assets	442,719		442,719
Total assets	1,318,608		1,318,608
Contract liabilities	58,307		58,307
Total current liabilities	204,285		204,285
Deferred tax liabilities	64,608		64,608
Total liabilities	517,159		517,159
Retained earnings	650,645		650,645
Total shareholders' equity	801,449		801,449
Total liabilities and shareholders' equity	1,318,608		1,318,608
Consolidated Statements of Operations
Net sales	195,758		566,525
Cost of sales	120,792		354,666
Total costs and expenses	173,494		498,448
Earnings before income tax	22,264		68,077
Income tax expense (benefit)	4,426		13,152
Net earnings	$ 17,838		$ 54,925
Basic:
Net earnings	$ 0.69		$ 2.12
Diluted:
Net earnings	$ 0.69		$ 2.11
Consolidated Statements of Comprehensive Income
Net earnings	$ 17,838		$ 54,925
Comprehensive income	19,670		53,006
Consolidated Statements of Cash flows
Net earnings	$ 17,838		54,925
Adjustments to reconcile net earnings to net cash provided by operating activities:
Change in assets and liabilities			(40,595)
Net cash provided by operating activities			$ 37,041