Financial Instruments and Risk Management (Narrative) (Details)	3 Months Ended		9 Months Ended
	Mar. 31, 2019 USD ($) bbl / d contract item	Mar. 31, 2018 USD ($) contract $ / bbl	Dec. 31, 2019 USD ($)	Dec. 31, 2018 item
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of foreign currency derivatives | contract	0	0
Amount of loss reclassified to interest expense	$ 700,000	$ 700,000
Number of offsetting positions | item	0			0
Scenario, Forecast [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative loss			$ 2,200,000
Commodity Derivative Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Daily production commitment (barrels per day)	0	21,000
Average price | $ / bbl		54.88
Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Loss deferred for fair value of interest rate derivative contracts, net of tax	$ 7,300,000
Income taxes on deferred loss on fair value of interest rate derivative contracts	$ 1,900,000
Notes Due 2022 [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Debt instrument term	10 years