Pension and Other Postretirement Benefits - Hierarchy of Fair Value of the Benefit Plan Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	$ 792,758	$ 808,635
NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	135,362	132,487
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	87,259	88,451
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	570,137	587,697
Corporate Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	350,394	365,723
Corporate Fixed Income Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	350,394	365,723
Value Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	74,070	76,186
Growth Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	49,438	43,880
Balanced Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	11,854	12,421
Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	83,361	85,138
Common Stock [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	83,361	85,138
US Government Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	62,381	72,817
US Government Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	62,381	72,817
Foreign Government Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	46,286	45,359
Foreign Government Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	46,286	45,359
Other Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	31,630	25,761
Other Fixed Income Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	31,630	25,761
Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	83,344	81,350
Other [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	3,898	3,313
Other [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans', Fair Value of Plan Assets	$ 79,446	$ 78,037