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Fair Value of Derivatives and Financial Instruments Fair Value, by Balance Sheet Grouping (Details) - USD ($) $ / shares in Units, $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Preferred Stock, Redemption Date | Oct. 01, 2026 |
Preferred Stock, Redemption Price Per Share | $ 50.00 |
Fixed Rate Debt |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Notes Payable Excluding Interest Rate Swaps and Cap Agreements | $ 3,160,000 | $ 3,000,000
Notes Payable, Fair Value Disclosure | 3,290,000 | 3,130,000
Floating Rate Debt |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Notes Payable Excluding Interest Rate Swaps and Cap Agreements | 1,300,000 | 1,500,000
Notes Payable, Fair Value Disclosure | 1,300,000 | 1,500,000
Fair Value, Measurements, Recurring [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Interest Rate Derivative Assets, at Fair Value | 3,551 | 2,364
Interest Rate Derivative Liabilities, at Fair Value | 1,316 | 7,562
Embedded Derivative, Fair Value of Embedded Derivative Asset | 21,169 | $ 10,783
Embedded Derivative, Gain on Embedded Derivative | 10,386 |
Business Combinations, Purchase Price Adjustment, Subsequent Adjustment | 1,600 |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Change in Unrealized Gain (Loss) | $ 8,800 |

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- Definition Fair value as of the balance sheet date of the embedded derivative or group of embedded derivatives classified as an asset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959 + Details
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- Definition Increase in the fair value of the embedded derivative or group of embedded derivatives included in earnings in the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959 + Details
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- Definition Amount of unrealized gain (loss) recognized in the income statement for a financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611 + Details
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