Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

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Fair value of all asset derivatives designated as cash flow hedging instruments.

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Fair value of all liability derivatives designated as cash flow hedging instruments.

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

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The amount of cash received during the period on settlement of a hedge.

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The premium (cost) of a hedge, net of any cash received on settlement during the period.

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The estimated value of gains (losses), net anticipated to be transferred in the future from accumulated other comprehensive income into earnings.

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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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The percentage of expected requirements covered by the aggregate notional amount of derivative contracts expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract as a percentage of expected need.

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Fixed price related to the price risk swap derivative.

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Amount before tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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Amount after tax of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

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Financial Instruments - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) MMBTU $ / MMBTU	Dec. 31, 2016	Mar. 31, 2016
Derivative [Line Items]
Amount of gains, net of income taxes, reclassified to earnings from change in fair value of derivatives component of accumulated other comprehensive loss	$ 100
Estimated reclassification of gains, net of income taxes, from the change in fair value of derivatives component of accumulated other comprehensive loss to earnings during the next twelve months	$ 200
Natural Gas [Member]
Derivative [Line Items]
Principal amount of natural gas swap agreements \| MMBTU	986,993
Hedged portion of exposure to natural gas price fluctuations (percent)	33.00%
Cash received	$ 200
Interest rate swap agreements [Member]
Derivative [Line Items]
Aggregate notional principal amount of outstanding interest rate swap agreements	100,000
Net payments under our interest rate swap agreements	100
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Derivative [Line Items]
Cash and cash equivalents	350,621
Carrying (Reported) Amount, Fair Value Disclosure [Member] \| Natural Gas [Member]
Derivative [Line Items]
Derivative Assets	402
Carrying (Reported) Amount, Fair Value Disclosure [Member] \| Interest rate swap agreements [Member]
Derivative [Line Items]
Derivative liabilities	92
Estimate of Fair Value, Fair Value Disclosure [Member]
Derivative [Line Items]
Cash and cash equivalents	350,621
Estimate of Fair Value, Fair Value Disclosure [Member] \| Natural Gas [Member]
Derivative [Line Items]
Derivative Assets	402
Estimate of Fair Value, Fair Value Disclosure [Member] \| Interest rate swap agreements [Member]
Derivative [Line Items]
Derivative liabilities	92
Bank debt [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Derivative [Line Items]
Long-Term Debt	400,183
Bank debt [Member] \| Estimate of Fair Value, Fair Value Disclosure [Member]
Derivative [Line Items]
Long-Term Debt	400,183
5% Senior Notes [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Derivative [Line Items]
Long-Term Debt	500,000
5% Senior Notes [Member] \| Estimate of Fair Value, Fair Value Disclosure [Member]
Derivative [Line Items]
Long-Term Debt	506,875
5 1/2% Senior Notes [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Derivative [Line Items]
Long-Term Debt	300,000
5 1/2% Senior Notes [Member] \| Estimate of Fair Value, Fair Value Disclosure [Member]
Derivative [Line Items]
Long-Term Debt	308,250
4 3/4% Senior Notes due 2025 [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Derivative [Line Items]
Long-Term Debt	300,000
4 3/4% Senior Notes due 2025 [Member] \| Estimate of Fair Value, Fair Value Disclosure [Member]
Derivative [Line Items]
Long-Term Debt	299,133
3 1/4% Senior Notes due 2025 [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member]
Derivative [Line Items]
Long-Term Debt	692,380
3 1/4% Senior Notes due 2025 [Member] \| Estimate of Fair Value, Fair Value Disclosure [Member]
Derivative [Line Items]
Long-Term Debt	$ 691,051
5% Senior Notes due 2020 [Member]
Derivative [Line Items]
Senior note interest rate (percent)	5.00%	5.00%	5.00%
5% Senior Notes due 2020 [Member] \| Senior Notes [Member]
Derivative [Line Items]
Senior note interest rate (percent)	5.00%
5 1/2% Senior Notes due 2022 [Member]
Derivative [Line Items]
Senior note interest rate (percent)	5.50%	5.50%	5.50%
5 1/2% Senior Notes due 2022 [Member] \| Senior Notes [Member]
Derivative [Line Items]
Senior note interest rate (percent)	5.50%
3 1/4% Senior Notes due 2025 [Member]
Derivative [Line Items]
Senior note interest rate (percent)	3.25%
4 3/4% Senior Notes due 2025 [Member]
Derivative [Line Items]
Senior note interest rate (percent)	4.75%
Minimum [Member] \| Natural Gas [Member]
Derivative [Line Items]
Natural gas fixed price \| $ / MMBTU	2.81
Maximum [Member] \| Natural Gas [Member]
Derivative [Line Items]
Natural gas fixed price \| $ / MMBTU	3.10
Accumulated Translation Adjustment [Member]
Derivative [Line Items]
Foreign currency (losses) of net investment hedges included in accumulated other comprehensive loss	$ (4,900)