SEGMENTS (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended		12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018
Financial information of reportable segment and the reconciliation of EBITDA to operating income
Costs and Expenses	$ 857,109		$ 745,185	$ 1,756,557	$ 1,527,871
Restructuring and Related Cost, Incurred Cost	11,832		11,396	15,879	29,758	$ 193,000
Gain (Loss) on Disposition of Business	(13,118)		(20,371)	(17,837)	(20,371)
Operating Income (Loss)	(2,001)		(29)	(68,549)	(1,026)
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component	(16,524)		(18,877)	(33,061)	(38,283)
Interest expense and other	28,714		25,375	54,206	46,393
Income (loss) from continuing operations before income taxes	(14,191)		(6,527)	(89,694)	(9,136)
Depreciation and amortization	38,134		40,868	76,945	79,999
Amortization of Acquired Contract Liabilities	16,804		27,898	34,038	57,371
EBITDA	32,447		33,312	79,436	41,973
Capital expenditures	12,054		10,690	24,254	22,775
Total assets	3,375,383			3,375,383		3,807,064
Revenues	855,108		745,156	1,688,008	1,526,845
Corporate Segment [Member]
Financial information of reportable segment and the reconciliation of EBITDA to operating income
Restructuring and Related Cost, Incurred Cost	2,767		4,159	2,767	14,708
Integrated Systems [Member]
Financial information of reportable segment and the reconciliation of EBITDA to operating income
Restructuring and Related Cost, Incurred Cost	2,275		1,180	3,056	2,341
Operating Income (Loss)	39,866		41,641	75,275	88,624
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component	446				(880)
Depreciation and amortization	7,384		9,588	14,939	19,539
Amortization of Acquired Contract Liabilities	8,768		9,299	17,617	16,602
EBITDA	38,482		41,930	72,597	91,561
Capital expenditures	3,828		1,455	5,437	4,020
Total assets	1,244,138			1,244,138		1,225,770
Revenues	260,717		233,765	501,756	471,900
Aerospace Structures [Member]
Financial information of reportable segment and the reconciliation of EBITDA to operating income
Restructuring and Related Cost, Incurred Cost	6,627		6,057	9,893	11,949
Operating Income (Loss)	(22,744)		(9,052)	(102,331)	(31,570)
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component			18,954		(37,926)
Depreciation and amortization	28,294		29,305	57,214	56,445
Amortization of Acquired Contract Liabilities	8,036		18,599	16,421	40,769
EBITDA	(2,486)		1,654	25,703	(15,894)
Capital expenditures	7,077		7,796	17,215	16,275
Total assets	1,812,835			1,812,835		2,260,416
Revenues	528,367		447,772	1,060,753	931,088
Product Support [Member]
Financial information of reportable segment and the reconciliation of EBITDA to operating income
Restructuring and Related Cost, Incurred Cost	163		0	163	760
Operating Income (Loss)	11,514		11,233	19,183	19,670
Depreciation and amortization	1,664		1,667	3,334	3,405
Amortization of Acquired Contract Liabilities	0
EBITDA	13,178		12,900	22,517	23,075
Capital expenditures	671		769	1,019	1,030
Total assets	283,938			283,938		281,101
Revenues	72,199		68,366	138,414	134,799
Elimination of inter-segment sales
Financial information of reportable segment and the reconciliation of EBITDA to operating income
Revenues	(6,175)		(4,747)	(12,915)	(10,942)
Corporate
Financial information of reportable segment and the reconciliation of EBITDA to operating income
Operating Income (Loss)	(30,637)		(43,851)	(60,676)	(77,750)
Depreciation and amortization	792		308	1,458	610
EBITDA	(16,727)		(23,172)	(41,381)	(56,769)
Capital expenditures	478		670	583	1,450
Total assets	34,472			34,472		39,777
Restructuring Charges [Member]
Financial information of reportable segment and the reconciliation of EBITDA to operating income
Restructuring and Related Cost, Incurred Cost	11,832		10,101	15,879	27,602
Restructuring Charges [Member] | Corporate Segment [Member]
Financial information of reportable segment and the reconciliation of EBITDA to operating income
Restructuring and Related Cost, Incurred Cost	2,767		4,159	2,767	14,708
Restructuring Charges [Member] | Integrated Systems [Member]
Financial information of reportable segment and the reconciliation of EBITDA to operating income
Restructuring and Related Cost, Incurred Cost	2,275		199	3,056	814
Restructuring Charges [Member] | Aerospace Structures [Member]
Financial information of reportable segment and the reconciliation of EBITDA to operating income
Restructuring and Related Cost, Incurred Cost	6,627		5,743	9,893	11,320
Restructuring Charges [Member] | Product Support [Member]
Financial information of reportable segment and the reconciliation of EBITDA to operating income
Restructuring and Related Cost, Incurred Cost	163		0	163	760
Guarantor Subsidiaries [Member]
Financial information of reportable segment and the reconciliation of EBITDA to operating income
Costs and Expenses	764,092		635,317	1,568,148	1,315,568
Gain (Loss) on Disposition of Business	(947)		0	(946)	0
Operating Income (Loss)	22,192		40,709	(16,969)	75,532
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component	(16,188)		(18,771)	(32,375)	(37,571)
Interest expense and other	5,201		2,606	9,282	5,386
Income (loss) from continuing operations before income taxes	(3,543)		19,148	(68,673)	28,971
Depreciation and amortization	32,743		36,402	66,659	71,175
Capital expenditures				21,145	19,215
Total assets	2,735,602			2,735,602		$ 3,123,793
Revenues	786,284		676,026	1,551,179	1,391,100
Accounting Standards Update 2017-07 [Member]
Financial information of reportable segment and the reconciliation of EBITDA to operating income
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income		$ 87,241
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component			(18,877)		(38,283)
Non-US [Member]
Financial information of reportable segment and the reconciliation of EBITDA to operating income
Revenues	$ 264,526		$ 166,637	$ 491,096	$ 345,044