CONSOLIDATING GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION (Details) - Summary of consolidated balance sheets - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
CURRENT ASSETS
Cash and equivalents	$ 218,089	$ 72,377
Accounts receivable, net of allowances	348,124	264,450
Contract assets, net of progress payments	84,426	105,111
Inventories	413,825	442,121
Prepaid and other current assets	46,897	40,799
Assets of discontinued operations	2,091	321
Total Current Assets	1,113,452	925,179
PROPERTY, PLANT AND EQUIPMENT, net	343,964
PROPERTY, PLANT AND EQUIPMENT, net		337,326
OPERATING LEASE RIGHT-OF-USE ASSETS	161,627
GOODWILL	442,643	437,067	$ 439,395
INTANGIBLE ASSETS, net	355,028	356,639
INTERCOMPANY RECEIVABLE	0	0
EQUITY INVESTMENTS IN SUBSIDIARIES	0	0
OTHER ASSETS	32,897	15,840
ASSETS OF DISCONTINUED OPERATIONS	6,406	2,888
Total Assets	2,456,017	2,074,939
CURRENT LIABILITIES
Notes payable and current portion of long-term debt	9,922	10,525
Accounts payable and accrued liabilities	403,679	375,241
Current portion of operating lease liabilities	31,848
Liabilities of discontinued operations	3,797	4,333
Total Current Liabilities	449,246	390,099
LONG-TERM DEBT, net	1,037,042	1,093,749
LONG-TERM OPERATING LEASE LIABILITIES	136,054
INTERCOMPANY PAYABLES	0	0
OTHER LIABILITIES	126,510	109,997
LIABILITIES OF DISCONTINUED OPERATIONS	7,014	3,331
Total Liabilities	1,755,866	1,597,176
SHAREHOLDERS’ EQUITY	700,151	477,763	$ 474,391	$ 398,808
Total Liabilities and Shareholders’ Equity	2,456,017	2,074,939
Parent Company
CURRENT ASSETS
Cash and equivalents	125,353	1,649
Accounts receivable, net of allowances	0	0
Contract assets, net of progress payments	0	0
Inventories	0	0
Prepaid and other current assets	14,650	8,238
Assets of discontinued operations	0	0
Total Current Assets	140,003	9,887
PROPERTY, PLANT AND EQUIPMENT, net	1,182
PROPERTY, PLANT AND EQUIPMENT, net		1,184
OPERATING LEASE RIGHT-OF-USE ASSETS	9,209
GOODWILL	0	0
INTANGIBLE ASSETS, net	93	93
INTERCOMPANY RECEIVABLE	568,124	5,834
EQUITY INVESTMENTS IN SUBSIDIARIES	1,724,821	1,628,031
OTHER ASSETS	12,585	8,182
ASSETS OF DISCONTINUED OPERATIONS	0	0
Total Assets	2,456,017	1,653,211
CURRENT LIABILITIES
Notes payable and current portion of long-term debt	0	0
Accounts payable and accrued liabilities	37,281	41,796
Current portion of operating lease liabilities	1,849
Liabilities of discontinued operations	0	0
Total Current Liabilities	39,130	41,796
LONG-TERM DEBT, net	995,636	1,040,449
LONG-TERM OPERATING LEASE LIABILITIES	8,415
INTERCOMPANY PAYABLES	683,076	71,634
OTHER LIABILITIES	29,609	21,569
LIABILITIES OF DISCONTINUED OPERATIONS	0	0
Total Liabilities	1,755,866	1,175,448
SHAREHOLDERS’ EQUITY	700,151	477,763
Total Liabilities and Shareholders’ Equity	2,456,017	1,653,211
Guarantor Companies
CURRENT ASSETS
Cash and equivalents	35,685	25,217
Accounts receivable, net of allowances	293,943	225,870
Contract assets, net of progress payments	80,572	104,109
Inventories	347,473	372,581
Prepaid and other current assets	25,974	25,610
Assets of discontinued operations	0	0
Total Current Assets	783,647	753,387
PROPERTY, PLANT AND EQUIPMENT, net	296,082
PROPERTY, PLANT AND EQUIPMENT, net		289,282
OPERATING LEASE RIGHT-OF-USE ASSETS	129,813
GOODWILL	377,060	375,734
INTANGIBLE ASSETS, net	217,317	224,275
INTERCOMPANY RECEIVABLE	704,415	881,110
EQUITY INVESTMENTS IN SUBSIDIARIES	784,644	581,438
OTHER ASSETS	25,953	10,010
ASSETS OF DISCONTINUED OPERATIONS	0	0
Total Assets	3,318,931	3,115,236
CURRENT LIABILITIES
Notes payable and current portion of long-term debt	2,855	3,075
Accounts payable and accrued liabilities	276,580	265,055
Current portion of operating lease liabilities	24,436
Liabilities of discontinued operations	0	0
Total Current Liabilities	303,871	268,130
LONG-TERM DEBT, net	15,992	3,119
LONG-TERM OPERATING LEASE LIABILITIES	110,061
INTERCOMPANY PAYABLES	397,846	466,792
OTHER LIABILITIES	85,731	73,411
LIABILITIES OF DISCONTINUED OPERATIONS	0	0
Total Liabilities	913,501	811,452
SHAREHOLDERS’ EQUITY	2,405,430	2,303,784
Total Liabilities and Shareholders’ Equity	3,318,931	3,115,236
Non-Guarantor Companies
CURRENT ASSETS
Cash and equivalents	57,051	45,511
Accounts receivable, net of allowances	54,181	38,580
Contract assets, net of progress payments	3,854	1,002
Inventories	66,352	69,540
Prepaid and other current assets	6,273	6,951
Assets of discontinued operations	2,091	321
Total Current Assets	189,802	161,905
PROPERTY, PLANT AND EQUIPMENT, net	46,700
PROPERTY, PLANT AND EQUIPMENT, net		46,860
OPERATING LEASE RIGHT-OF-USE ASSETS	22,605
GOODWILL	65,583	61,333
INTANGIBLE ASSETS, net	137,618	132,271
INTERCOMPANY RECEIVABLE	257,013	75,684
EQUITY INVESTMENTS IN SUBSIDIARIES	3,176,855	3,233,038
OTHER ASSETS	(5,641)	(2,352)
ASSETS OF DISCONTINUED OPERATIONS	6,406	2,888
Total Assets	3,896,941	3,711,627
CURRENT LIABILITIES
Notes payable and current portion of long-term debt	7,067	7,450
Accounts payable and accrued liabilities	89,818	68,390
Current portion of operating lease liabilities	5,563
Liabilities of discontinued operations	3,797	4,333
Total Current Liabilities	106,245	80,173
LONG-TERM DEBT, net	25,414	50,181
LONG-TERM OPERATING LEASE LIABILITIES	17,578
INTERCOMPANY PAYABLES	459,599	444,557
OTHER LIABILITIES	11,170	15,017
LIABILITIES OF DISCONTINUED OPERATIONS	7,014	3,331
Total Liabilities	627,020	593,259
SHAREHOLDERS’ EQUITY	3,269,921	3,118,368
Total Liabilities and Shareholders’ Equity	3,896,941	3,711,627
Elimination
CURRENT ASSETS
Cash and equivalents	0	0
Accounts receivable, net of allowances	0	0
Contract assets, net of progress payments	0	0
Inventories	0	0
Prepaid and other current assets	0	0
Assets of discontinued operations	0	0
Total Current Assets	0	0
PROPERTY, PLANT AND EQUIPMENT, net	0
PROPERTY, PLANT AND EQUIPMENT, net		0
OPERATING LEASE RIGHT-OF-USE ASSETS	0
GOODWILL	0	0
INTANGIBLE ASSETS, net	0	0
INTERCOMPANY RECEIVABLE	(1,529,552)	(962,628)
EQUITY INVESTMENTS IN SUBSIDIARIES	(5,686,320)	(5,442,507)
OTHER ASSETS	0	0
ASSETS OF DISCONTINUED OPERATIONS	0	0
Total Assets	(7,215,872)	(6,405,135)
CURRENT LIABILITIES
Notes payable and current portion of long-term debt	0	0
Accounts payable and accrued liabilities	0	0
Current portion of operating lease liabilities	0
Liabilities of discontinued operations	0	0
Total Current Liabilities	0	0
LONG-TERM DEBT, net	0	0
LONG-TERM OPERATING LEASE LIABILITIES	0
INTERCOMPANY PAYABLES	(1,540,521)	(982,983)
OTHER LIABILITIES	0	0
LIABILITIES OF DISCONTINUED OPERATIONS	0	0
Total Liabilities	(1,540,521)	(982,983)
SHAREHOLDERS’ EQUITY	(5,675,351)	(5,422,152)
Total Liabilities and Shareholders’ Equity	$ (7,215,872)	$ (6,405,135)