Investments in Non-Consolidated Subsidiaries (Details 3) (White Cliffs Pipeline L L C [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
White Cliffs Pipeline L L C [Member]
Summarized income statement information
Equity Method Investment, Summarized Financial Information, Revenue	$ 31,453	$ 28,522	$ 92,238	$ 76,910
Equity Method Investment, Summarized Financial Information, Operating, General and Administrative Expenses	5,141	3,857	14,433	11,382
Equity Method Investment, Summarized Financial Information, Depreciation and Amortization Expense	4,720	4,995	14,150	14,964
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	$ 21,579	$ 19,670	$ 63,642	$ 50,564