SELECTED CONSOLIDATING FINANCIAL STATEMENTS OF PARENT, GUARANTORS AND NON-GUARANTORS - Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Consolidating Financial Statements, Captions
Cash and cash equivalents	$ 53,594			$ 92,807	$ 28,664			$ 35,819
Trade and other receivables, net	300,730			373,590
Contract with Customer, Asset, Net, Current	241,875			326,667
Inventory, Net	473,863			413,560
Prepaid and other current assets	26,133			34,446
Total current assets	1,096,195			1,241,070
Property and equipment, net	433,475			543,710
Goodwill and other intangible assets, net	978,481			1,014,179
Other, net	117,235			55,615
Intercompany investments and advances	0			0
Total assets	2,625,386			2,854,574
Current liabilities:
Current portion of long-term debt	7,795			8,201
Accounts payable	379,989			433,783
Accrued expenses	231,065			239,572
Accrued Liabilities and Other Liabilities	495,528			533,291
Total current liabilities	883,312			975,275
Long-term debt, less current portion	1,400,893			1,480,620
Intercompany advances	0			0
Accrued pension and other postretirement benefits, noncurrent	496,284			540,479
Deferred income taxes and other	377,794			431,513
Total stockholders’ equity	(532,897)	$ (590,824)	$ (557,919)	(573,313)	(276,497)	$ (238,051)	$ (226,581)	450,534
Total liabilities and stockholders' equity	2,625,386			2,854,574
Rotable Assets	55,430			57,282
Consolidation, Eliminations [Member]
Consolidating Financial Statements, Captions
Cash and cash equivalents	0			0	0			0
Trade and other receivables, net	0			0
Contract with Customer, Asset, Net, Current	0			0
Inventory, Net	0			0
Prepaid and other current assets	0			0
Total current assets	0			0
Property and equipment, net	0			0
Goodwill and other intangible assets, net	0			0
Other, net	0			0
Intercompany investments and advances	(1,487,410)			(1,431,234)
Total assets	(1,487,410)			(1,431,234)
Current liabilities:
Current portion of long-term debt	0			0
Accounts payable	0			0
Accrued Liabilities and Other Liabilities	0			0
Total current liabilities	0			0
Long-term debt, less current portion	0			0
Intercompany advances	(2,651,730)			(2,652,609)
Accrued pension and other postretirement benefits, noncurrent	0			0
Deferred income taxes and other	0			0
Total stockholders’ equity	1,164,320			1,221,375
Total liabilities and stockholders' equity	(1,487,410)			(1,431,234)
Parent
Consolidating Financial Statements, Captions
Cash and cash equivalents	19,319			70,192	0			44
Trade and other receivables, net	8,391			10,150
Contract with Customer, Asset, Net, Current	0			0
Inventory, Net	0			0
Prepaid and other current assets	12,031			22,152
Total current assets	39,741			102,494
Property and equipment, net	10,227			11,276
Goodwill and other intangible assets, net	0			0
Other, net	27,536			14,630
Intercompany investments and advances	1,353,361			1,112,100
Total assets	1,430,865			1,240,500
Current liabilities:
Current portion of long-term debt	1,900			1,904
Accounts payable	5,301			6,571
Accrued Liabilities and Other Liabilities	52,940			58,301
Total current liabilities	60,141			66,776
Long-term debt, less current portion	1,319,259			1,469,543
Intercompany advances	562,434			262,718
Accrued pension and other postretirement benefits, noncurrent	5,889			6,067
Deferred income taxes and other	16,039			8,709
Total stockholders’ equity	(532,897)			(573,313)
Total liabilities and stockholders' equity	1,430,865			1,240,500
Guarantor Subsidiaries [Member]
Consolidating Financial Statements, Captions
Cash and cash equivalents	0			429	61			0
Trade and other receivables, net	85,193			123,153
Contract with Customer, Asset, Net, Current	237,383			322,698
Inventory, Net	393,159			339,038
Prepaid and other current assets	7,330			7,611
Total current assets	723,065			792,929
Property and equipment, net	343,902			449,489
Goodwill and other intangible assets, net	877,509			912,279
Other, net	59,031			34,664
Intercompany investments and advances	44,362			230,437
Total assets	2,047,869			2,419,798
Current liabilities:
Current portion of long-term debt	5,888			6,297
Accounts payable	343,977			396,542
Accrued Liabilities and Other Liabilities	411,624			445,542
Total current liabilities	761,489			848,381
Long-term debt, less current portion	6,616			11,077
Intercompany advances	1,827,108			2,017,003
Accrued pension and other postretirement benefits, noncurrent	490,395			534,412
Deferred income taxes and other	331,845			408,838
Total stockholders’ equity	(1,369,584)			(1,399,913)
Total liabilities and stockholders' equity	2,047,869			2,419,798
Non-Guarantor Subsidiaries
Consolidating Financial Statements, Captions
Cash and cash equivalents	34,275			22,186	$ 28,603			$ 35,775
Trade and other receivables, net	207,146			240,287
Contract with Customer, Asset, Net, Current	4,492			3,969
Inventory, Net	80,704			74,522
Prepaid and other current assets	6,772			4,683
Total current assets	333,389			345,647
Property and equipment, net	79,346			82,945
Goodwill and other intangible assets, net	100,972			101,900
Other, net	30,668			6,321
Intercompany investments and advances	89,687			88,697
Total assets	634,062			625,510
Current liabilities:
Current portion of long-term debt	7			0
Accounts payable	30,711			30,670
Accrued Liabilities and Other Liabilities	30,964			29,448
Total current liabilities	61,682			60,118
Long-term debt, less current portion	75,018			0
Intercompany advances	262,188			372,888
Accrued pension and other postretirement benefits, noncurrent	0			0
Deferred income taxes and other	29,910			13,966
Total stockholders’ equity	205,264			178,538
Total liabilities and stockholders' equity	$ 634,062			$ 625,510