Fair Value Measurements - Narrative (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maximum borrowing capacity	$ 1,500,000,000.0
Estimated fair value of total debt	3,510,217,000	$ 2,803,267,000
Carrying value of total debt	3,289,459,000	$ 2,793,343,000
EQM
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maximum borrowing capacity	$ 750,000,000