CONSOLIDATING GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Oct. 01, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018
CURRENT ASSETS
Cash and equivalents	$ 71,999				$ 72,377
Accounts receivable, net of allowances	359,464				264,450
Contract costs and recognized income not yet billed, net of progress payments	92,143				105,111
Inventories, net	411,028				442,121
Prepaid and other current assets	51,365				40,799
Assets of discontinued operations	1,951				321
Total Current Assets	987,950				925,179
PROPERTY, PLANT AND EQUIPMENT, net	335,318
PROPERTY, PLANT AND EQUIPMENT, net					337,326
OPERATING LEASE RIGHT-OF-USE ASSETS	154,955			$ 163,552
GOODWILL	439,667				437,067
INTANGIBLE ASSETS, net	354,384				356,639
INTERCOMPANY RECEIVABLE	0				0
EQUITY INVESTMENTS IN SUBSIDIARIES	0				0
OTHER ASSETS	31,860				15,840
ASSETS OF DISCONTINUED OPERATIONS	6,086				2,888
Total Assets	2,310,220				2,074,939
CURRENT LIABILITIES
Notes payable and current portion of long-term debt	9,235				10,525
Accounts payable and accrued liabilities	394,188				375,241
Current portion of operating lease liabilities	29,018
Liabilities of discontinued operations	3,730				4,333
Total Current Liabilities	436,171				390,099
LONG-TERM DEBT, net	1,123,365				1,093,749
LONG-TERM OPERATING LEASE LIABILITIES	131,650
INTERCOMPANY PAYABLES	0				0
OTHER LIABILITIES	104,298				109,997
LIABILITIES OF DISCONTINUED OPERATIONS	6,281				3,331
Total Liabilities	1,801,765				1,597,176
SHAREHOLDERS’ EQUITY	508,455	$ 476,454	$ 494,693		477,763	$ 488,165	$ 474,284	$ 471,561	$ 474,391
Total Liabilities and Shareholders’ Equity	2,310,220				2,074,939
Reportable Legal Entities | Parent Company
CURRENT ASSETS
Cash and equivalents	4,727				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	19,519				8,238
Assets of discontinued operations	0				0
Total Current Assets	24,246				9,887
PROPERTY, PLANT AND EQUIPMENT, net	1,232
PROPERTY, PLANT AND EQUIPMENT, net					1,184
OPERATING LEASE RIGHT-OF-USE ASSETS	9,633
GOODWILL	0				0
INTANGIBLE ASSETS, net	93				93
INTERCOMPANY RECEIVABLE	16,555				5,834
EQUITY INVESTMENTS IN SUBSIDIARIES	1,702,746				1,628,031
OTHER ASSETS	12,228				8,182
ASSETS OF DISCONTINUED OPERATIONS	0				0
Total Assets	1,766,733				1,653,211
CURRENT LIABILITIES
Notes payable and current portion of long-term debt	0				0
Accounts payable and accrued liabilities	58,619				41,796
Current portion of operating lease liabilities	1,842
Liabilities of discontinued operations	0				0
Total Current Liabilities	60,461				41,796
LONG-TERM DEBT, net	1,087,135				1,040,449
LONG-TERM OPERATING LEASE LIABILITIES	8,886
INTERCOMPANY PAYABLES	77,139				71,634
OTHER LIABILITIES	24,657				21,569
LIABILITIES OF DISCONTINUED OPERATIONS	0				0
Total Liabilities	1,258,278				1,175,448
SHAREHOLDERS’ EQUITY	508,455				477,763
Total Liabilities and Shareholders’ Equity	1,766,733				1,653,211
Reportable Legal Entities | Guarantor Companies
CURRENT ASSETS
Cash and equivalents	19,697				25,217
Accounts receivable, net of allowances	307,625				227,069
Contract costs and recognized income not yet billed, net of progress payments	89,526				104,109
Inventories, net	347,703				372,839
Prepaid and other current assets	24,144				25,754
Assets of discontinued operations	0				0
Total Current Assets	788,695				754,988
PROPERTY, PLANT AND EQUIPMENT, net	289,224
PROPERTY, PLANT AND EQUIPMENT, net					289,282
OPERATING LEASE RIGHT-OF-USE ASSETS	124,566
GOODWILL	375,734				375,734
INTANGIBLE ASSETS, net	219,056				224,275
INTERCOMPANY RECEIVABLE	679,666				864,884
EQUITY INVESTMENTS IN SUBSIDIARIES	766,863				581,438
OTHER ASSETS	39,491				24,635
ASSETS OF DISCONTINUED OPERATIONS	0				0
Total Assets	3,283,295				3,115,236
CURRENT LIABILITIES
Notes payable and current portion of long-term debt	2,973				3,075
Accounts payable and accrued liabilities	426,260				266,411
Current portion of operating lease liabilities	22,229
Liabilities of discontinued operations	0				0
Total Current Liabilities	451,462				269,486
LONG-TERM DEBT, net	10,258				3,119
LONG-TERM OPERATING LEASE LIABILITIES	106,552
INTERCOMPANY PAYABLES	254,479				457,265
OTHER LIABILITIES	77,228				81,582
LIABILITIES OF DISCONTINUED OPERATIONS	0				0
Total Liabilities	899,979				811,452
SHAREHOLDERS’ EQUITY	2,383,316				2,303,784
Total Liabilities and Shareholders’ Equity	3,283,295				3,115,236
Reportable Legal Entities | Non-Guarantor Companies
CURRENT ASSETS
Cash and equivalents	47,575				45,511
Accounts receivable, net of allowances	217,590				38,580
Contract costs and recognized income not yet billed, net of progress payments	2,617				1,002
Inventories, net	63,903				69,540
Prepaid and other current assets	5,068				6,951
Assets of discontinued operations	1,951				321
Total Current Assets	338,704				161,905
PROPERTY, PLANT AND EQUIPMENT, net	44,862
PROPERTY, PLANT AND EQUIPMENT, net					46,860
OPERATING LEASE RIGHT-OF-USE ASSETS	20,756
GOODWILL	63,933				61,333
INTANGIBLE ASSETS, net	135,235				132,271
INTERCOMPANY RECEIVABLE	84,671				75,684
EQUITY INVESTMENTS IN SUBSIDIARIES	3,154,553				3,233,038
OTHER ASSETS	(5,638)				(2,352)
ASSETS OF DISCONTINUED OPERATIONS	6,086				2,888
Total Assets	3,843,162				3,711,627
CURRENT LIABILITIES
Notes payable and current portion of long-term debt	6,262				7,450
Accounts payable and accrued liabilities	72,451				68,390
Current portion of operating lease liabilities	4,947
Liabilities of discontinued operations	3,730				4,333
Total Current Liabilities	87,390				80,173
LONG-TERM DEBT, net	25,972				50,181
LONG-TERM OPERATING LEASE LIABILITIES	16,212
INTERCOMPANY PAYABLES	467,463				444,557
OTHER LIABILITIES	10,242				15,017
LIABILITIES OF DISCONTINUED OPERATIONS	6,281				3,331
Total Liabilities	613,560				593,259
SHAREHOLDERS’ EQUITY	3,229,602				3,118,368
Total Liabilities and Shareholders’ Equity	3,843,162				3,711,627
Elimination
CURRENT ASSETS
Cash and equivalents	0				0
Accounts receivable, net of allowances	(165,751)				(1,199)
Contract costs and recognized income not yet billed, net of progress payments	0				0
Inventories, net	(578)				(258)
Prepaid and other current assets	2,634				(144)
Assets of discontinued operations	0				0
Total Current Assets	(163,695)				(1,601)
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	(780,892)				(946,402)
EQUITY INVESTMENTS IN SUBSIDIARIES	(5,624,162)				(5,442,507)
OTHER ASSETS	(14,221)				(14,625)
ASSETS OF DISCONTINUED OPERATIONS	0				0
Total Assets	(6,582,970)				(6,405,135)
CURRENT LIABILITIES
Notes payable and current portion of long-term debt	0				0
Accounts payable and accrued liabilities	(163,142)				(1,356)
Current portion of operating lease liabilities	0
Liabilities of discontinued operations	0				0
Total Current Liabilities	(163,142)				(1,356)
LONG-TERM DEBT, net	0				0
LONG-TERM OPERATING LEASE LIABILITIES	0
INTERCOMPANY PAYABLES	(799,081)				(973,456)
OTHER LIABILITIES	(7,829)				(8,171)
LIABILITIES OF DISCONTINUED OPERATIONS	0				0
Total Liabilities	(970,052)				(982,983)
SHAREHOLDERS’ EQUITY	(5,612,918)				(5,422,152)
Total Liabilities and Shareholders’ Equity	$ (6,582,970)				$ (6,405,135)