Assets Held for Sale - Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Jan. 15, 2015
Income Statement Balance Sheet And Additional Disclosures Assets Held For Sale Not Part Of Disposal Group [Line Items]
Assets held for sale		$ 41,211,000
Depreciation		$ 0
Minimum Development Agreement Period	90 days
Cross Valley
Income Statement Balance Sheet And Additional Disclosures Assets Held For Sale Not Part Of Disposal Group [Line Items]
Assets held for sale			$ 34,200,000
GSEC
Income Statement Balance Sheet And Additional Disclosures Assets Held For Sale Not Part Of Disposal Group [Line Items]
Assets held for sale			$ 7,000,000