Pension and Other Postretirement Benefit Plans - Schedule of Components of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Curtailment loss	$ 28,000
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 383	$ 600	$ 760	$ 1,181
Interest cost		16,100	17,427	32,186	36,089
Expected return on plan assets		(34,136)	(35,500)	(68,241)	(70,618)
Amortization of prior service credits		243	(233)	485	(512)
Amortization of net loss		7,807	6,808	15,605	13,019
Curtailment loss			23,476		23,476
Special termination benefits			11,642		11,642
Net periodic benefit income		(9,603)	24,220	(19,205)	14,277
Other postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost			18		62
Interest cost		28	614	56	1,478
Amortization of prior service credits		(1,276)	(1,156)	(2,552)	(2,320)
Amortization of net loss		(1,191)	(1,547)	(2,382)	(3,989)
Curtailment loss			(49,491)		(49,491)
Net periodic benefit income		$ (2,439)	$ (51,562)	$ (4,878)	$ (54,260)