Segments - Schedule of Selected Financial Information for Each Reportable Segment and Reconciliation of EBITDAP to Operating Income (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended				9 Months Ended
		Sep. 30, 2019	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019		Dec. 31, 2020	Dec. 31, 2019		Mar. 31, 2020	[1]
Segment Reporting Information [Line Items]
Net sales to external customers			$ 425,994		$ 704,666	[1]	$ 1,402,886	$ 2,207,007	[1]
Segment profit and reconciliation to consolidated income before income taxes:
Adjusted EBITDAP			61,407		89,272		131,067	250,126
Reconciliation of segment profit to income (loss) before income taxes
Depreciation and amortization			(22,119)		(29,843)	[1]	(72,819)	(104,112)	[1]
Interest expense and other, net			(44,881)		(33,178)	[1]	(132,344)	(96,069)	[1]
Corporate expenses			(8,483)		(13,848)		(42,027)	(42,709)
Share-based compensation expense			(3,679)		(2,955)		(9,086)	(8,245)
Loss on sale of assets and businesses		$ 10,000	(45,273)		(60,019)	[1]	(46,020)	(55,190)	[1]
Amortization of acquired contract liabilities			6,867		16,597		35,017	56,153
Non-service defined benefit income			12,432		14,799	[1]	37,275	56,025	[1]
Union represented employee incentives					(1,400)			(7,071)
Legal judgment gain, net	[1]				3,857			9,257
Impairment of long-lived assets				$ (252,382)			(252,382)
Impairment of rotable inventory			(23,689)				(23,689)
Loss before income taxes			(67,418)		(16,718)		(375,008)	58,165
Total capital expenditures			6,184		10,255		18,988	27,250
Total assets			2,401,922				2,401,922			$ 2,980,333
Systems & Support [Member]
Segment Reporting Information [Line Items]
Intersegment sales (eliminated in consolidation)			482		1,717		2,888	4,118
Reconciliation of segment profit to income (loss) before income taxes
Amortization of acquired contract liabilities			4,306		8,377		11,569	26,126
Aerospace Structures [Member]
Segment Reporting Information [Line Items]
Intersegment sales (eliminated in consolidation)			54		1,513		1,469	5,106
Reconciliation of segment profit to income (loss) before income taxes
Amortization of acquired contract liabilities			2,561		8,220		23,448	30,027
Corporate & Eliminations [Member]
Segment Reporting Information [Line Items]
Net sales to external customers			(536)		(3,230)		(4,357)	(9,224)
Reconciliation of segment profit to income (loss) before income taxes
Depreciation and amortization			(989)		(847)		(2,652)	(2,533)
Total capital expenditures			158		416		801	980
Total assets			451,824				451,824
Operating Segments [Member] | Systems & Support [Member]
Segment Reporting Information [Line Items]
Net sales to external customers			263,638		337,207		755,290	1,001,384
Segment profit and reconciliation to consolidated income before income taxes:
Adjusted EBITDAP			46,746		57,132		110,983	162,008
Reconciliation of segment profit to income (loss) before income taxes
Depreciation and amortization			(8,353)		(8,075)		(24,830)	(24,314)
Total capital expenditures			2,308		3,929		11,819	12,355
Total assets			1,463,017				1,463,017
Operating Segments [Member] | Aerospace Structures [Member]
Segment Reporting Information [Line Items]
Net sales to external customers			162,356		367,459		647,596	1,205,623
Segment profit and reconciliation to consolidated income before income taxes:
Adjusted EBITDAP			14,661		32,140		20,084	88,118
Reconciliation of segment profit to income (loss) before income taxes
Depreciation and amortization			(12,777)		(20,921)		(45,337)	(77,265)
Total capital expenditures			3,718		$ 5,910		6,368	$ 13,915
Total assets			$ 487,081				$ 487,081

[1] As adjusted; refer to Note 1.