Restatement Restated Balance Sheet (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jul. 01, 2012
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated depreciation	$ (1,197,126)	$ (1,162,213)	$ (1,119,899)
Total assets	2,080,895	2,019,865	2,133,529
Deferred Tax Liability	154,292	153,792	134,108
Limited Partners' Equity	49,986	177,660	88,757
As previously filed [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated depreciation			(1,111,530)
Total assets			2,141,898
Deferred Tax Liability			137,288
Limited Partners' Equity			93,946
Correction [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated depreciation			(8,369)
Total assets			(8,369)
Deferred Tax Liability			(3,180)
Limited Partners' Equity			$ (5,189)