Financial Instruments and Risk Management (Narrative) (Details) $ in Millions	1 Months Ended	6 Months Ended	9 Months Ended
	Oct. 30, 2019 barrels_per_day $ / bbl	Dec. 31, 2019 USD ($)	Sep. 30, 2020 bbl / d	Sep. 30, 2019 USD ($) bbl / d OffsettingPosition contract Acquisition $ / bbl	Sep. 30, 2018 barrels_per_day contract $ / bbl	Jun. 30, 2020 $ / bbl	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				$ 2.2
Number of businesses acquired (in acquisitions) | Acquisition				2
Number of offsetting positions (in positions)				0			0
Scenario, Forecast
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative loss		$ 0.7
Commodity derivative contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Daily production commitment (barrels per day)				35,000	21,000
Average Forward Price (in dollars per barrel) | $ / bbl				60.51	54.88
Interest Rate Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Loss deferred for fair value of interest rate derivative contracts, net of tax				$ 6.1
Income taxes on deferred loss on fair value of interest rate derivative contracts				$ 1.6
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)	45,000		35,000
Average Forward Price (in dollars per barrel) | $ / bbl	56.42					57.59