Equity Method Investments - Activity Related to Equity Method Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity Method Investments
Balance at beginning of period	$ 68,029	$ 26,892	$ 6,915
Contributions	29,073	38,057	18,875
Earnings (loss) on equity method investments	6,415	3,080	1,102
Balance at end of period	103,517	68,029	26,892
Constitution Pipeline Company, LLC
Equity Method Investments
Balance at beginning of period	64,268	26,892	6,915
Contributions	19,625	34,200	18,875
Earnings (loss) on equity method investments	6,452	3,176	1,102
Balance at end of period	90,345	64,268	26,892
Meade Pipeline Co LLC
Equity Method Investments
Balance at beginning of period	3,761	0	0
Contributions	9,448	3,857	0
Earnings (loss) on equity method investments	(37)	(96)	0
Balance at end of period	$ 13,172	$ 3,761	$ 0