SELECTED CONSOLIDATING FINANCIAL STATEMENTS OF PARENT, GUARANTORS AND NON-GUARANTORS - Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Consolidating Financial Statements, Captions
Cash and cash equivalents	$ 24,852		$ 92,807	$ 33,227		$ 35,819
Trade and other receivables, net	342,306		373,590
Contract with Customer, Asset, Net, Current	300,670		326,667
Inventory, Net	454,402		413,560
Prepaid and other current assets	20,854		34,446
Total current assets	1,143,084		1,241,070
Property and equipment, net	502,990		543,710
Goodwill and other intangible assets, net	984,898		1,014,179
Other, net	130,831		55,615
Intercompany investments and advances	0		0
Total assets	2,761,803		2,854,574
Current liabilities:
Current portion of long-term debt	7,759		8,201
Accounts payable	418,706		433,783
Accrued expenses	221,966		239,572
Accrued Liabilities and Other Liabilities	498,933		533,291
Total current liabilities	925,398		975,275
Long-term debt, less current portion	1,460,774		1,480,620
Intercompany advances	0		0
Accrued pension and other postretirement benefits, noncurrent	554,400		540,479
Deferred income taxes and other	412,055		431,513
Total stockholders’ equity	(590,824)	$ (557,919)	(573,313)	(238,051)	$ (226,581)	450,534
Total liabilities and stockholders' equity	2,761,803		2,854,574
Rotable Assets	56,864		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	(1,429,042)		(1,431,234)
Total assets	(1,429,042)		(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	(2,652,253)		(2,652,609)
Accrued pension and other postretirement benefits, noncurrent	0		0
Deferred income taxes and other	0		0
Total stockholders’ equity	1,223,211		1,221,375
Total liabilities and stockholders' equity	(1,429,042)		(1,431,234)
Parent
Consolidating Financial Statements, Captions
Cash and cash equivalents	55		70,192	79		44
Trade and other receivables, net	9,159		10,150
Contract with Customer, Asset, Net, Current	0		0
Inventory, Net	0		0
Prepaid and other current assets	9,116		22,152
Total current assets	18,330		102,494
Property and equipment, net	10,642		11,276
Goodwill and other intangible assets, net	0		0
Other, net	28,162		14,630
Intercompany investments and advances	1,274,684		1,112,100
Total assets	1,331,818		1,240,500
Current liabilities:
Current portion of long-term debt	1,735		1,904
Accounts payable	2,972		6,571
Accrued Liabilities and Other Liabilities	40,933		58,301
Total current liabilities	45,640		66,776
Long-term debt, less current portion	1,386,539		1,469,543
Intercompany advances	467,160		262,718
Accrued pension and other postretirement benefits, noncurrent	5,923		6,067
Deferred income taxes and other	17,380		8,709
Total stockholders’ equity	(590,824)		(573,313)
Total liabilities and stockholders' equity	1,331,818		1,240,500
Guarantor Subsidiaries [Member]
Consolidating Financial Statements, Captions
Cash and cash equivalents	167		429	237		0
Trade and other receivables, net	103,937		123,153
Contract with Customer, Asset, Net, Current	294,773		322,698
Inventory, Net	375,848		339,038
Prepaid and other current assets	6,829		7,611
Total current assets	781,554		792,929
Property and equipment, net	414,005		449,489
Goodwill and other intangible assets, net	889,099		912,279
Other, net	72,511		34,664
Intercompany investments and advances	65,297		230,437
Total assets	2,222,466		2,419,798
Current liabilities:
Current portion of long-term debt	6,024		6,297
Accounts payable	383,213		396,542
Accrued Liabilities and Other Liabilities	429,312		445,542
Total current liabilities	818,549		848,381
Long-term debt, less current portion	8,307		11,077
Intercompany advances	1,891,936		2,017,003
Accrued pension and other postretirement benefits, noncurrent	548,477		534,412
Deferred income taxes and other	363,681		408,838
Total stockholders’ equity	(1,408,484)		(1,399,913)
Total liabilities and stockholders' equity	2,222,466		2,419,798
Non-Guarantor Subsidiaries
Consolidating Financial Statements, Captions
Cash and cash equivalents	24,630		22,186	$ 32,911		$ 35,775
Trade and other receivables, net	229,210		240,287
Contract with Customer, Asset, Net, Current	5,897		3,969
Inventory, Net	78,554		74,522
Prepaid and other current assets	4,909		4,683
Total current assets	343,200		345,647
Property and equipment, net	78,343		82,945
Goodwill and other intangible assets, net	95,799		101,900
Other, net	30,158		6,321
Intercompany investments and advances	89,061		88,697
Total assets	636,561		625,510
Current liabilities:
Current portion of long-term debt	0		0
Accounts payable	32,521		30,670
Accrued Liabilities and Other Liabilities	28,688		29,448
Total current liabilities	61,209		60,118
Long-term debt, less current portion	65,928		0
Intercompany advances	293,157		372,888
Accrued pension and other postretirement benefits, noncurrent	0		0
Deferred income taxes and other	30,994		13,966
Total stockholders’ equity	185,273		178,538
Total liabilities and stockholders' equity	$ 636,561		$ 625,510