Employee Benefit Plans - Schedule of Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017
Pension
Defined Benefit Plan Disclosure [Line Items]
Unrecognized prior service costs	$ 0	$ 0	$ 0	$ 0
Unrecognized net actuarial income	68,752	59,579	61,731	55,438
Total accumulated other comprehensive income	68,752	59,579	61,731	55,438
RIM
Defined Benefit Plan Disclosure [Line Items]
Unrecognized prior service costs	0	0	0	0
Unrecognized net actuarial income	5,577	3,748	5,515	4,725
Total accumulated other comprehensive income	5,577	3,748	5,515	4,725
Post-retirement
Defined Benefit Plan Disclosure [Line Items]
Unrecognized prior service costs	0	0	(106)	(140)
Unrecognized net actuarial income	7,221	4,226	6,395	4,611
Total accumulated other comprehensive income	$ 7,221	$ 4,226	$ 6,289	$ 4,471