Investments in Non-Consolidated Subsidiaries - Summarized financial information - Glass Mountain (Details) (Glass Mountain Pipeline LLC [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2014
Glass Mountain Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Summarized Financial Information, Revenue	$ 8,891	$ 12,744
Equity Method Investment, Summarized Financial Information, Operating, General and Administrative Expenses	1,158	2,008
Equity Method Investment, Summarized Financial Information, Depreciation and Amortization Expense	3,770	6,118
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	$ 3,962	$ 4,615