Derivative Instruments - Narrative (Details) MMBTU in Millions	1 Months Ended		3 Months Ended		9 Months Ended
	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) MMBTU	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) MMBTU	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Apr. 30, 2019 USD ($)
Derivative [Line Items]
Cash received (paid) in settlement of commodity derivative instruments			$ 90,310,000	$ 57,041,000	$ 383,727,000	$ 26,331,000
Interest Rate Swap
Derivative [Line Items]
Derivative notional amount			$ 575,625,000		575,625,000		$ 160,000,000
Interest Rate Swap on Revolving Credit Facility | Long
Derivative [Line Items]
Term of derivative contract	4 years
Put option	0.00%
Derivative notional amount	$ 250,000,000
Interest Rate Swap on Line of Credit | Long
Derivative [Line Items]
Put option	0.25%
NYMEX Natural Gas Hedges | Natural Gas
Derivative [Line Items]
Cash received (paid) in settlement of commodity derivative instruments					$ 5,851,000
Nonmonetary notional amount | MMBTU			8		8
NYMEX Commodity Swaps | Natural Gas
Derivative [Line Items]
Cash received (paid) in settlement of commodity derivative instruments					$ 54,982,000
Line of Credit
Derivative [Line Items]
Credit facility, face amount	$ 175,000,000
Revolving Credit Facility
Derivative [Line Items]
Credit facility, face amount		$ 160,000,000						$ 2,100,000,000
Credit facility, modification period		3 years