CONSOLIDATING GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
CURRENT ASSETS
Cash and equivalents	$ 64,792	$ 72,377
Accounts receivable, net of allowances	272,572	264,450
Contract costs and recognized income not yet billed, net of progress payments	96,826	105,111
Inventories, net	467,069	442,121
Prepaid and other current assets	44,374	40,799
Assets of discontinued operations	321	321
Total Current Assets	945,954	925,179
PROPERTY, PLANT AND EQUIPMENT, net	332,148	337,326
OPERATING LEASE RIGHT-OF-USE ASSETS	154,379
GOODWILL	446,590	437,067
INTANGIBLE ASSETS, net	357,743	356,639
INTERCOMPANY RECEIVABLE	0	0
EQUITY INVESTMENTS IN SUBSIDIARIES	0	0
OTHER ASSETS	18,105	15,840
ASSETS OF DISCONTINUED OPERATIONS	2,883	2,888
Total Assets	2,257,802	2,074,939
CURRENT LIABILITIES
Notes payable and current portion of long-term debt	9,451	10,525
Accounts payable and accrued liabilities	346,981	375,241
Current portion of operating lease liabilities	28,292
Liabilities of discontinued operations	3,787	4,333
Total Current Liabilities	388,511	390,099
LONG-TERM DEBT, net	1,137,134	1,093,749
LONG-TERM OPERATING LEASE LIABILITIES	130,949
INTERCOMPANY PAYABLES	0	0
OTHER LIABILITIES	103,299	109,997
LIABILITIES OF DISCONTINUED OPERATIONS	3,216	3,331
Total Liabilities	1,763,109	1,597,176
SHAREHOLDERS’ EQUITY	494,693	477,763	$ 471,561	$ 474,391
Total Liabilities and Shareholders’ Equity	2,257,802	2,074,939
Reportable Legal Entities | Parent Company
CURRENT ASSETS
Cash and equivalents	3,070	1,649
Accounts receivable, net of allowances	0	0
Contract costs and recognized income not yet billed, net of progress payments	0	0
Inventories, net	0	0
Prepaid and other current assets	11,041	8,238
Assets of discontinued operations	0	0
Total Current Assets	14,111	9,887
PROPERTY, PLANT AND EQUIPMENT, net	1,313	1,184
OPERATING LEASE RIGHT-OF-USE ASSETS	10,483
GOODWILL	0	0
INTANGIBLE ASSETS, net	92	93
INTERCOMPANY RECEIVABLE	40,433	5,834
EQUITY INVESTMENTS IN SUBSIDIARIES	1,654,370	1,628,031
OTHER ASSETS	8,206	8,182
ASSETS OF DISCONTINUED OPERATIONS	0	0
Total Assets	1,729,008	1,653,211
CURRENT LIABILITIES
Notes payable and current portion of long-term debt	0	0
Accounts payable and accrued liabilities	48,147	41,796
Current portion of operating lease liabilities	1,823
Liabilities of discontinued operations	0	0
Total Current Liabilities	49,970	41,796
LONG-TERM DEBT, net	1,091,638	1,040,449
LONG-TERM OPERATING LEASE LIABILITIES	9,816
INTERCOMPANY PAYABLES	64,689	71,634
OTHER LIABILITIES	18,202	21,569
LIABILITIES OF DISCONTINUED OPERATIONS	0	0
Total Liabilities	1,234,315	1,175,448
SHAREHOLDERS’ EQUITY	494,693	477,763
Total Liabilities and Shareholders’ Equity	1,729,008	1,653,211
Reportable Legal Entities | Guarantor Companies
CURRENT ASSETS
Cash and equivalents	25,532	25,217
Accounts receivable, net of allowances	241,261	227,069
Contract costs and recognized income not yet billed, net of progress payments	94,672	104,109
Inventories, net	391,447	372,839
Prepaid and other current assets	26,573	25,754
Assets of discontinued operations	0	0
Total Current Assets	779,485	754,988
PROPERTY, PLANT AND EQUIPMENT, net	284,774	289,282
OPERATING LEASE RIGHT-OF-USE ASSETS	125,259
GOODWILL	375,734	375,734
INTANGIBLE ASSETS, net	222,536	224,275
INTERCOMPANY RECEIVABLE	907,715	864,884
EQUITY INVESTMENTS IN SUBSIDIARIES	495,645	581,438
OTHER ASSETS	24,343	24,635
ASSETS OF DISCONTINUED OPERATIONS	0	0
Total Assets	3,215,491	3,115,236
CURRENT LIABILITIES
Notes payable and current portion of long-term debt	2,589	3,075
Accounts payable and accrued liabilities	299,912	266,411
Current portion of operating lease liabilities	22,389
Liabilities of discontinued operations	0	0
Total Current Liabilities	324,890	269,486
LONG-TERM DEBT, net	2,743	3,119
LONG-TERM OPERATING LEASE LIABILITIES	106,191
INTERCOMPANY PAYABLES	527,147	457,265
OTHER LIABILITIES	79,514	81,582
LIABILITIES OF DISCONTINUED OPERATIONS	0	0
Total Liabilities	1,040,485	811,452
SHAREHOLDERS’ EQUITY	2,175,006	2,303,784
Total Liabilities and Shareholders’ Equity	3,215,491	3,115,236
Reportable Legal Entities | Non-Guarantor Companies
CURRENT ASSETS
Cash and equivalents	36,190	45,511
Accounts receivable, net of allowances	32,533	38,580
Contract costs and recognized income not yet billed, net of progress payments	2,154	1,002
Inventories, net	75,869	69,540
Prepaid and other current assets	6,906	6,951
Assets of discontinued operations	321	321
Total Current Assets	153,973	161,905
PROPERTY, PLANT AND EQUIPMENT, net	46,061	46,860
OPERATING LEASE RIGHT-OF-USE ASSETS	18,637
GOODWILL	70,856	61,333
INTANGIBLE ASSETS, net	135,115	132,271
INTERCOMPANY RECEIVABLE	105,239	75,684
EQUITY INVESTMENTS IN SUBSIDIARIES	3,353,794	3,233,038
OTHER ASSETS	0	(2,352)
ASSETS OF DISCONTINUED OPERATIONS	2,883	2,888
Total Assets	3,886,558	3,711,627
CURRENT LIABILITIES
Notes payable and current portion of long-term debt	6,862	7,450
Accounts payable and accrued liabilities	0	68,390
Current portion of operating lease liabilities	4,080
Liabilities of discontinued operations	3,787	4,333
Total Current Liabilities	14,729	80,173
LONG-TERM DEBT, net	42,753	50,181
LONG-TERM OPERATING LEASE LIABILITIES	14,942
INTERCOMPANY PAYABLES	490,808	444,557
OTHER LIABILITIES	13,754	15,017
LIABILITIES OF DISCONTINUED OPERATIONS	3,216	3,331
Total Liabilities	580,202	593,259
SHAREHOLDERS’ EQUITY	3,306,356	3,118,368
Total Liabilities and Shareholders’ Equity	3,886,558	3,711,627
Elimination
CURRENT ASSETS
Cash and equivalents	0	0
Accounts receivable, net of allowances	(1,222)	(1,199)
Contract costs and recognized income not yet billed, net of progress payments	0	0
Inventories, net	(247)	(258)
Prepaid and other current assets	(146)	(144)
Assets of discontinued operations	0	0
Total Current Assets	(1,615)	(1,601)
PROPERTY, PLANT AND EQUIPMENT, net	0	0
OPERATING LEASE RIGHT-OF-USE ASSETS	0
GOODWILL	0	0
INTANGIBLE ASSETS, net	0	0
INTERCOMPANY RECEIVABLE	(1,053,387)	(946,402)
EQUITY INVESTMENTS IN SUBSIDIARIES	(5,503,809)	(5,442,507)
OTHER ASSETS	(14,444)	(14,625)
ASSETS OF DISCONTINUED OPERATIONS	0	0
Total Assets	(6,573,255)	(6,405,135)
CURRENT LIABILITIES
Notes payable and current portion of long-term debt	0	0
Accounts payable and accrued liabilities	(1,078)	(1,356)
Current portion of operating lease liabilities	0
Liabilities of discontinued operations	0	0
Total Current Liabilities	(1,078)	(1,356)
LONG-TERM DEBT, net	0	0
LONG-TERM OPERATING LEASE LIABILITIES	0
INTERCOMPANY PAYABLES	(1,082,644)	(973,456)
OTHER LIABILITIES	(8,171)	(8,171)
LIABILITIES OF DISCONTINUED OPERATIONS	0	0
Total Liabilities	(1,091,893)	(982,983)
SHAREHOLDERS’ EQUITY	(5,481,362)	(5,422,152)
Total Liabilities and Shareholders’ Equity	$ (6,573,255)	$ (6,405,135)