Restatement of Consolidated Financial Statements (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Accumulated Depreciation, Depletion and Amortization, Sale or Disposal of Property, Plant and Equipment		$ 8,800,000
Depreciation and amortization	126,306,000	125,837,000	128,856,000
Gain Loss on Retirement and Impairment of Property Plant and Equipment	30,336,000	11,355,000	62,752,000
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(1,162,213,000)	(1,071,978,000)
Assets	2,019,865,000	2,047,168,000
Deferred Tax Liability	153,792,000	130,427,000
Limited Partners' Capital Account	177,660,000	160,068,000
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	133,614,000	73,173,000	(30,382,000)
Income Tax Expense (Benefit)	31,757,000	7,877,000	2,670,000
Net income (loss)	101,857,000	65,296,000	(33,052,000)
Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic	1.83	1.18	(0.60)
Net income (loss) per limited partner unit	1.82	1.17	(0.60)
Restatement Adjustment [Member]
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Depreciation and amortization	0	2,032,000	2,060,000
Gain Loss on Retirement and Impairment of Property Plant and Equipment	0	0	0
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	0	(18,599,000)
Assets	0
Deferred Tax Liability	0
Limited Partners' Capital Account	0	(1,679,000)
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	0	(2,032,000)	(2,060,000)
Income Tax Expense (Benefit)	0	(620,000)	(575,000)
Net income (loss)	0	(1,412,000)	(1,485,000)
Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic	0.00	(0.02)	(0.03)
Net income (loss) per limited partner unit	0.00	(0.02)	(0.03)
Material restatement adjustment [Member]
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Depreciation and amortization	(1,033,000)	0	0
Gain Loss on Retirement and Impairment of Property Plant and Equipment	0	(8,790,000)	0
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(7,757,000)	(8,790,000)
Assets	(7,757,000)	(8,790,000)
Deferred Tax Liability	(2,948,000)	(3,340,000)
Limited Partners' Capital Account	(4,809,000)	(5,450,000)
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	1,033,000	(8,790,000)	0
Income Tax Expense (Benefit)	392,000	(3,340,000)	0
Net income (loss)	641,000	(5,450,000)	0
Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic	0.01	(0.10)	0.00
Net income (loss) per limited partner unit	0.01	(0.10)	0.00
Scenario, Previously Reported [Member]
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Depreciation and amortization	127,339,000	123,805,000	126,796,000
Gain Loss on Retirement and Impairment of Property Plant and Equipment	30,336,000	2,565,000	62,752,000
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(1,154,456,000)	(1,044,589,000)
Assets	2,027,622,000
Deferred Tax Liability	156,740,000
Limited Partners' Capital Account	182,469,000	135,446,000
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	132,581,000	83,995,000	(28,322,000)
Income Tax Expense (Benefit)	31,365,000	11,837,000	3,245,000
Net income (loss)	101,216,000	72,158,000	(31,567,000)
Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic	1.82	1.30	(0.57)
Net income (loss) per limited partner unit	1.81	1.29	(0.57)
Scenario, Previously Reported 2012 10K [Member]
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Depreciation and amortization	127,339,000	125,837,000	128,856,000
Gain Loss on Retirement and Impairment of Property Plant and Equipment	(30,336,000)	(2,565,000)	(62,752,000)
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(1,154,456,000)	(1,063,188,000)
Assets	2,027,622,000	2,055,958,000
Deferred Tax Liability	156,740,000	133,767,000
Limited Partners' Capital Account	182,469,000	165,518,000
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	132,581,000	81,963,000	(30,382,000)
Income Tax Expense (Benefit)	31,365,000	11,217,000	2,670,000
Net income (loss)	$ 101,216,000	$ 70,746,000	$ (33,052,000)
Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic	1.82	1.28	(0.60)
Net income (loss) per limited partner unit	1.81	1.27	(0.60)