Long-Term Debt - Outstanding Debt (Detail) - USD ($)	3 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 695,000,000	$ 625,000,000
Unamortized Debt Issuance Expense	(7,232,000)	(7,613,000)
Carrying Amount	687,768,000	617,387,000
Debt, fair value	$ 596,000,000	594,400,000
Amended Credit Facility
Debt Instrument [Line Items]
Maturity Date	Sep. 14, 2023
Debt Instrument, Face Amount	$ 70,000,000	0
Unamortized Debt Issuance Expense	0	0
Carrying Amount	70,000,000	0
7.0% Senior Notes
Debt Instrument [Line Items]
Debt Instrument, Face Amount	350,000,000	350,000,000
Unamortized Debt Issuance Expense	(3,000,000)	(3,210,000)
Carrying Amount	$ 347,000,000	346,790,000
Debt, stated interest rate	7.00%
Debt, fair value	$ 332,700,000	329,700,000
8.75% Senior Notes
Debt Instrument [Line Items]
Debt Instrument, Face Amount	275,000,000	275,000,000
Unamortized Debt Issuance Expense	(4,232,000)	(4,403,000)
Carrying Amount	$ 270,768,000	270,597,000
Debt, stated interest rate	8.75%
Debt, fair value	$ 263,300,000	264,700,000
Lease Financing Obligation
Debt Instrument [Line Items]
Debt Instrument, Face Amount	0	1,859,000
Unamortized Debt Issuance Expense	0	0
Carrying Amount	0	1,859,000
Debt, fair value		1,800,000
Long-term Debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount	695,000,000	626,859,000
Unamortized Debt Issuance Expense	(7,232,000)	(7,613,000)
Carrying Amount	687,768,000	619,246,000
Current Portion of Long-Term Debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount	0	1,859,000
Unamortized Debt Issuance Expense	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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- Definition

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

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- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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-Publisher FASB
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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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