Schedule of Other Changes in Plan Assets and Benefit Obligation Recognized (Detail) - USD ($) $ in Thousands	4 Months Ended	5 Months Ended	12 Months Ended
	Jul. 31, 2017	Dec. 31, 2017	Dec. 31, 2018	Mar. 31, 2017
Pension Plans, Defined Benefit
Schedule Of Accumulated Benefit Obligations In Excess Of Fair Value Of Plan Assets And Amounts Recognized In Balance Sheet And In Other Comprehensive Income Loss [Line Items]
Net (gain) loss		$ 1,939	$ (3,441)
Curtailment (gain) loss			(335)
Total recognized in other comprehensive (income) loss, before tax		1,939	(3,776)
Net of tax		1,939	(3,776)
Pension Plans, Defined Benefit | Predecessor
Schedule Of Accumulated Benefit Obligations In Excess Of Fair Value Of Plan Assets And Amounts Recognized In Balance Sheet And In Other Comprehensive Income Loss [Line Items]
Net (gain) loss	$ 1,877			$ 3,821
Fresh-start accounting fair value adjustment	(22,333)
Recognized actuarial loss	(748)			(1,785)
Total recognized in other comprehensive (income) loss, before tax	(21,204)			2,036
Net of tax	(21,204)			1,323
Other Pension Plan
Schedule Of Accumulated Benefit Obligations In Excess Of Fair Value Of Plan Assets And Amounts Recognized In Balance Sheet And In Other Comprehensive Income Loss [Line Items]
Net (gain) loss		325	229
Prior service (cost) credit		(1,861)
Amortization of prior service cost			1,861
Recognized actuarial loss			(554)
Total recognized in other comprehensive (income) loss, before tax		(1,536)	1,536
Net of tax		$ (1,536)	$ 1,536
Other Pension Plan | Predecessor
Schedule Of Accumulated Benefit Obligations In Excess Of Fair Value Of Plan Assets And Amounts Recognized In Balance Sheet And In Other Comprehensive Income Loss [Line Items]
Net (gain) loss	207			(285)
Amortization of prior service cost	927			4,346
Fresh-start accounting fair value adjustment	19,055
Recognized actuarial loss	335			1,138
Total recognized in other comprehensive (income) loss, before tax	20,524			5,199
Net of tax	$ 20,524			$ 3,379