Schedule of Net Periodic Benefit Cost (Detail) - Pension Plan And Supplemental Plan - USD ($) $ in Thousands	4 Months Ended	5 Months Ended	12 Months Ended
	Jul. 31, 2017	Dec. 31, 2017	Dec. 31, 2018	Mar. 31, 2017
Net Period Benefit Cost Assumptions [Line Items]
Service cost		$ 546	$ 294
Interest cost		1,599	3,605
Expected return on plan assets		(882)	(2,042)
Administrational expenses		19	36
Payroll tax of net pension costs		29	42
Amortization of net actuarial losses		131	30
Curtailment (gain) loss		(99)	335
Net periodic pension cost		$ 1,343	$ 2,300
Predecessor
Net Period Benefit Cost Assumptions [Line Items]
Service cost	$ 393			$ 1,182
Interest cost	1,313			3,814
Expected return on plan assets	(691)			(2,246)
Administrational expenses	3			28
Payroll tax of net pension costs				56
Amortization of net actuarial losses				32
Recognized actuarial loss	748			1,785
Net periodic pension cost	$ 1,766			$ 4,651