Long-term Debt - Opco Credit Agreement (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 28, 2012	Jun. 18, 2011
Debt Instrument [Line Items]
Long-term debt		$ 2,146,599,000	$ 2,198,148,000
Loss on extinguishment of debt	(146,800,000)	(4,132,000)	(146,787,000)	(51,796,000)
Opco [Member]
Debt Instrument [Line Items]
Loss on extinguishment of debt				51,800,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long-term debt		0	0
Revolving Credit Facility [Member] | Opco and GVR [Member]
Debt Instrument [Line Items]
Revolving credit facility, maximum borrowing capacity					200,000,000
Revolving Credit Facility [Member] | Opco [Member]
Debt Instrument [Line Items]
Revolving credit facility, maximum borrowing capacity						25,000,000
Revolving Credit Facility [Member] | GVR Lenders [Member]
Debt Instrument [Line Items]
Revolving credit facility, maximum borrowing capacity						10,000,000
Term Loan Facility [Member]
Debt Instrument [Line Items]
Long-term debt		1,503,831,000	1,561,415,000
Term Loan Facility [Member] | Opco and GVR [Member]
Debt Instrument [Line Items]
Long-term debt, aggregate principal amount					575,000,000
Term Loan Facility [Member] | Opco [Member]
Debt Instrument [Line Items]
Long-term debt, aggregate principal amount						435,700,000
Used to Repay Original OPCO Credit Facility [Member] | Joint Term Loan [Member] | Opco and GVR [Member]
Debt Instrument [Line Items]
Long-term debt					$ 517,000,000