Financial Instruments and Risk Management (Narrative) (Details) barrels_per_day in Thousands, $ in Millions	6 Months Ended				24 Months Ended
	Dec. 31, 2020 barrels_per_day $ / bbl	Jun. 30, 2020 USD ($) barrels_per_day OffsettingPosition contract $ / bbl	Dec. 31, 2019 barrels_per_day OffsettingPosition $ / bbl	Jun. 30, 2019 USD ($) barrels_per_day contract	Dec. 31, 2019 Acquisition OffsettingPosition $ / bbl	Dec. 31, 2021 $ / bbl
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of foreign currency derivatives (in contracts) | contract		0		0
Amount of loss reclassified to interest expense		$ 0.8		$ 1.5
Income taxes on deferred loss on fair value of interest rate derivative contracts		2.3
Derivative loss		$ 0.8
Number of businesses acquired (in acquisitions) | Acquisition					2
Number of offsetting positions (in offsetting positions) | OffsettingPosition		0	0		0
Commodity derivative contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Daily production commitment (barrels per day) | barrels_per_day		45	20	20
Average forward price (in dollars per barrel) | $ / bbl		56.42	63.64		63.64
Interest Rate Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Income taxes on deferred loss on fair value of interest rate derivative contracts		$ 0.6
Notes Due 2022
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Debt instrument term		10 years
Forecast | Commodity derivative contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Average forward price (in dollars per barrel) | $ / bbl	60.10					41.54
Forecast | Commodity derivative contracts | Subsequent Event
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Daily production commitment (barrels per day) | barrels_per_day	2