Summary of Significant Accounting Policies (Fair Value of Financial Instruments) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Investments	$ 3,158,312,000	$ 3,180,095,000
Total return swap	1,650,000	0
Investments [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Investments	3,158,312,000	3,180,095,000
Interest Rate Swap [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Interest rate swap agreements, liabilities	0	103,000
Secured Debt [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instrument, fair value	140,000,000	140,000,000
Unsecured Debt [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instrument, fair value	50,000,000	0
Equity Contract [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Equity contracts	$ 140,000	$ 175,000

Equity Contracts Financial Instruments Liabilities Fair Value Disclosure

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value of asset associated with financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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- Definition

Sum of the carrying amounts as of the balance sheet date of all investments.

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