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Summary of Significant Accounting Policies (Details 3) (USD $)	3 Months Ended		15 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Dec. 31, 2014
Internal-Use Software
Impairment of internal-use software		$ 922,000
Revenue Recognition
Increase to rental revenue			100,000
Allowance for doubtful accounts (in dollars)	160,000		160,000	112,000
Asset Retirement and Environmental Remediation Obligations
Asset retirement and environmental remediation obligations	2,300,000us-gaap_AssetRetirementObligation		2,300,000us-gaap_AssetRetirementObligation	2,300,000us-gaap_AssetRetirementObligation
Income taxes
Minimum percentage of distribution of taxable income to qualify as REIT	90.00%
Percentage of distribution of taxable income as per company policy	100.00%
Provision for federal income taxes	0us-gaap_CurrentFederalTaxExpenseBenefit
Liabilities for uncertain positions	$ 0cor_LiabilityForUncertainTaxPositions		$ 0cor_LiabilityForUncertainTaxPositions