Senior Bank Debt (Details) (USD $)
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12 Months Ended | ||||
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Dec. 31, 2013
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Dec. 31, 2012
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Dec. 31, 2013
Line of Credit [Member]
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Dec. 31, 2012
Line of Credit [Member]
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Apr. 30, 2013
Senior unsecured revolving credit facility [Member]
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|
Deb Instrument [Line Items] | |||||
Maximum borrowing capacity | $ 1,250,000,000 | ||||
Line of credit facility amount outstanding | 525,000,000 | 325,000,000 | |||
Weighted average interest rate | 1.95% | 2.77% | |||
Commitment fee amount | $ 3,200,000 | $ 3,700,000 |