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			6 Months Ended
		Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019		Sep. 30, 2020	Sep. 30, 2019		Mar. 31, 2020	[1]
Segment Reporting Information [Line Items]
Net sales to external customers			$ 481,815	$ 772,110	[1]	$ 976,892	$ 1,502,341	[1]
Segment profit and reconciliation to consolidated income before income taxes:
Adjusted EBITDAP			31,208	78,246		69,660	160,854
Reconciliation of segment profit to income (loss) before income taxes
Depreciation and amortization			(22,098)	(30,219)	[1]	(50,700)	(74,269)	[1]
Interest expense and other, net			(52,506)	(35,400)	[1]	(87,463)	(62,891)	[1]
Corporate expenses			(15,483)	(14,436)		(33,544)	(28,861)
Share-based compensation expense			(2,621)	(2,864)		(5,407)	(5,290)
Gain (Loss) on sale of assets and businesses		$ 10,000	(747)	7,965	[1]	(747)	4,829	[1]
Amortization of acquired contract liabilities			17,163	22,616		28,150	39,556
Non-service defined benefit income			12,427	27,824	[1]	24,843	41,226	[1]
Union represented employee incentives				(5,671)			(5,671)
Legal judgment gain, net	[1]			5,400			5,400
Impairment of long-lived assets						(252,382)
Income before income taxes			(32,657)	53,461		(307,590)	74,883
Total capital expenditures			5,081	8,905		12,804	16,995
Total assets			2,533,425			2,533,425			$ 2,980,333
Systems & Support [Member]
Segment Reporting Information [Line Items]
Intersegment sales (eliminated in consolidation)			534	1,563		2,406	2,401
Reconciliation of segment profit to income (loss) before income taxes
Amortization of acquired contract liabilities			3,544	9,624		7,263	17,749
Aerospace Structures [Member]
Segment Reporting Information [Line Items]
Intersegment sales (eliminated in consolidation)			600	1,878		1,415	3,592
Reconciliation of segment profit to income (loss) before income taxes
Amortization of acquired contract liabilities			13,619	12,992		20,887	21,807
Corporate & Eliminations [Member]
Segment Reporting Information [Line Items]
Net sales to external customers			(1,134)	(3,441)		(3,821)	(5,993)
Reconciliation of segment profit to income (loss) before income taxes
Depreciation and amortization			(807)	(852)		(1,663)	(1,686)
Total capital expenditures			232	331		643	564
Total assets			537,236			537,236
Operating Segments [Member] | Systems & Support [Member]
Segment Reporting Information [Line Items]
Net sales to external customers			253,637	351,409		491,652	664,176
Segment profit and reconciliation to consolidated income before income taxes:
Adjusted EBITDAP			34,169	60,795		64,237	104,876
Reconciliation of segment profit to income (loss) before income taxes
Depreciation and amortization			(8,121)	(8,082)		(16,477)	(16,239)
Total capital expenditures			3,228	4,542		9,511	8,426
Total assets			1,410,292			1,410,292
Operating Segments [Member] | Aerospace Structures [Member]
Segment Reporting Information [Line Items]
Net sales to external customers			228,178	420,701		485,240	838,165
Segment profit and reconciliation to consolidated income before income taxes:
Adjusted EBITDAP			(2,961)	17,451		5,423	55,978
Reconciliation of segment profit to income (loss) before income taxes
Depreciation and amortization			(13,170)	(21,285)		(32,560)	(56,344)
Total capital expenditures			1,621	$ 4,032		2,650	$ 8,005
Total assets			$ 585,897			$ 585,897

[1] As adjusted; refer to Note 1.