Annual report pursuant to Section 13 and 15(d)

PENSION AND OTHER POSTRETIREMENT PLANS - Net Periodic Pension and Other Postretirement Benefit Cost (Details)

v3.10.0.1
PENSION AND OTHER POSTRETIREMENT PLANS - Net Periodic Pension and Other Postretirement Benefit Cost (Details) - USD ($)
$ in Thousands
 12 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2016
Pension      
Defined Benefit Plan Disclosure [Line Items]      
Service cost $ 8,159 $ 8,553 $ 7,446
Interest cost 8,210 7,362 9,725
Expected return on plan assets (10,136) (9,249) (9,625)
Prior service cost (138) (181) (183)
Net actuarial loss (gain) 7,018 10,034 7,468
Net benefit cost 13,113 16,519 14,831
Other Postretirement      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 335 392 402
Interest cost 631 626 845
Expected return on plan assets 0 0 0
Prior service cost (195) (195) (195)
Net actuarial loss (gain) 0 0 0
Net benefit cost $ 771 $ 823 $ 1,052