Financial Instruments and Risk Management (Narrative) (Details) bbl / d in Thousands, $ in Millions	1 Months Ended	2 Months Ended	3 Months Ended		12 Months Ended
	Apr. 30, 2020 bbl / d $ / bbl	Jun. 30, 2020 bbl / d $ / bbl	Mar. 31, 2020 USD ($) bbl / d contract OffsettingPosition	Mar. 31, 2019 USD ($) barrels_per_day contract	Dec. 31, 2019 item Acquisition	Dec. 31, 2020 $ / bbl
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of foreign currency derivatives | contract			0	0
Amount of loss reclassified to interest expense			$ 0.4	$ 0.7
Income taxes on deferred loss on fair value of interest rate derivative contracts			2.6
Derivative loss			$ 1.1
Number of businesses acquired (in acquisitions) | Acquisition					2
Number of offsetting positions (in positions)			0		0
Commodity derivative contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Daily production commitment (barrels per day)			45	0
Interest Rate Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Income taxes on deferred loss on fair value of interest rate derivative contracts			$ 0.7
Notes Due 2022
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Debt instrument term			10 years
Subsequent Event | Commodity derivative contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Daily production commitment (barrels per day) | bbl / d	65
Average forward price (in dollars per barrel) | $ / bbl	56.42
Forecast | Subsequent Event | Commodity derivative contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Daily production commitment (barrels per day) | bbl / d		45
Average forward price (in dollars per barrel) | $ / bbl		47.20				56.42