Postretirement Benefit Plans (Schedule of Fair Value of Pension Assets) (Details) - Insurance contracts $ in Thousands	Mar. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 40,601
Quoted Prices in Active Markets for Identical Assets Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Significant Other Observable Inputs Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	40,601
Significant Unobservable Inputs Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0