Taxes Other Than Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Taxes Other Than Income Taxes [Line Items]
taxes other than income	$ 12,815	$ 13,384	$ 37,943	$ 39,884
Property [Member]
Taxes Other Than Income Taxes [Line Items]
taxes other than income	6,860	6,246	17,938	19,040
Capital Stock [Member]
Taxes Other Than Income Taxes [Line Items]
taxes other than income	(274)	488	749	1,599
Gross Receipts, Excise And Franchise [Member]
Taxes Other Than Income Taxes [Line Items]
taxes other than income	2,727	3,211	8,476	8,842
Payroll [Member]
Taxes Other Than Income Taxes [Line Items]
taxes other than income	1,650	1,682	5,913	5,747
Other [Member]
Taxes Other Than Income Taxes [Line Items]
taxes other than income	$ 1,852	$ 1,757	$ 4,867	$ 4,656