Long-Term Debt - Outstanding Debt (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Principal	$ 765,000,000	$ 625,000,000
Debt Issuance Costs	(6,089,000)	(7,613,000)
Carrying Amount	758,911,000	617,387,000
Debt Instrument, Fair Value Disclosure	586,200,000	594,400,000
Amended Credit Facility
Debt Instrument [Line Items]
Principal	140,000,000	0
Debt Issuance Costs	0	0
Carrying Amount	140,000,000	0
Debt Instrument, Fair Value Disclosure	140,000,000.0	0
7.0% Senior Notes
Debt Instrument [Line Items]
Principal	350,000,000.0	350,000,000
Debt Issuance Costs	(2,372,000)	(3,210,000)
Carrying Amount	$ 347,628,000	346,790,000
Debt, stated interest rate	7.00%		7.00%
Debt Instrument, Fair Value Disclosure	$ 335,000,000.0	329,700,000
8.75% Senior Notes
Debt Instrument [Line Items]
Principal	275,000,000	275,000,000
Debt Issuance Costs	(3,717,000)	(4,403,000)
Carrying Amount	$ 271,283,000	270,597,000
Debt, stated interest rate	8.75%
Debt Instrument, Fair Value Disclosure	$ 251,200,000	264,700,000
Lease Financing Obligation
Debt Instrument [Line Items]
Principal	0	1,859,000
Debt Issuance Costs	0	0
Carrying Amount	0	1,859,000
Debt Instrument, Fair Value Disclosure		1,800,000
Total Debt
Debt Instrument [Line Items]
Principal	765,000,000	626,859,000
Debt Issuance Costs	(6,089,000)	(7,613,000)
Carrying Amount	758,911,000	619,246,000
Current Portion of Long-Term Debt
Debt Instrument [Line Items]
Principal	0	1,859,000
Debt Issuance Costs	0	0
Carrying Amount	$ 0	$ 1,859,000

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Face (par) amount of debt instrument at time of issuance.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Contractual interest rate for funds borrowed, under the debt agreement.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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