Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

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

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

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The aggregate net gain (loss) on price risk derivatives included in earnings in the period.

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DERIVATIVE FINANCIAL INSTRUMENTS (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended		0 Months Ended
	Dec. 27, 2014 MMBTU	Dec. 28, 2013 MMBTU	Sep. 10, 2014	Sep. 22, 2014	Sep. 27, 2014	Dec. 31, 2011	Jun. 25, 2011
Derivative Instrument
Annual consolidated natural gas purchase requirements (in MMBtu)	1,079,000
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (134,433)	$ (47,685)
5.00% senior unsecured notes due 2044
Derivative Instrument
Aggregate principal amount	250,000			250,000
Interest rate on notes (as a percent)	5.00%	5.00%		5.00%
5.25% senior unsecured notes due 2054
Derivative Instrument
Aggregate principal amount	250,000			250,000
Interest rate on notes (as a percent)	5.25%	5.25%		5.25%
6.625% senior unsecured notes due in April 2020
Derivative Instrument
Aggregate principal amount	250,200
Interest rate on notes (as a percent)	6.625%	6.625%		6.625%
Debt Repurchase Amount				199,800	199,800
Parent
Derivative Instrument
Accumulated Other Comprehensive Income (Loss), Net of Tax	(134,433)	(47,685)
Natural Gas Price Swap
Derivative Instrument
Quantities of natural gas (in MMBtu)	80,000	120,000
Unrealized gain (loss)	(53)	73
Interest rate contract \| Cash flow hedging
Derivative Instrument
Payment to counterparty to settle the derivative contract			4,837
Interest rate contract \| Cash flow hedging \| 5.00% senior unsecured notes due 2044
Derivative Instrument
Notional amount of derivative instrument					125,000
Interest rate contract \| Cash flow hedging \| 5.25% senior unsecured notes due 2054
Derivative Instrument
Notional amount of derivative instrument					125,000
Interest rate contract \| Cash flow hedging \| 6.625% senior unsecured notes due in April 2020
Derivative Instrument
Aggregate principal amount						150,000
Interest rate on notes (as a percent)						6.625%
Notional amount of derivative instrument							130,000
Loss on interest rate cash flow hedge derivative, recorded in accumulated other comprehensive income					983
Debt Repurchase Amount					199,800
Forward contracts \| Cash flow hedging
Derivative Instrument
Unrealized gain (loss)	424
Accumulated Other Comprehensive Income (Loss), Net of Tax	242
Notional amount of derivative instrument	14,757
Forward contracts \| Fair Value Hedging
Derivative Instrument
Unrealized gain (loss)		475
Notional amount of derivative instrument		$ 28,032