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Equity (Narrative) (Details) $ / shares in Units, $ in Millions |  |  |  |  |  |  |  |  |  |  |  | 1 Months Ended | 12 Months Ended |  |  |
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Dec. 15, 2020 USD ($) $ / shares | Sep. 16, 2020 $ / shares shares | Dec. 11, 2019 USD ($) $ / shares | Nov. 21, 2019 USD ($) $ / shares | Aug. 01, 2019 | Dec. 10, 2018 $ / shares shares | Nov. 06, 2018 USD ($) $ / shares | Nov. 01, 2018 USD ($) | Jun. 11, 2018 USD ($) | May 04, 2018 USD ($) $ / shares shares | May 03, 2017 USD ($) | Sep. 03, 2020 $ / shares shares | Sep. 13, 2019 $ / shares shares | Dec. 31, 2018 USD ($) shares | Dec. 31, 2020 USD ($) $ / shares shares | Dec. 31, 2019 USD ($) $ / shares shares | Dec. 31, 2018 USD ($) $ / shares shares | Jun. 15, 2023 $ / shares | Dec. 05, 2018 shares | Dec. 31, 2017 shares
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, shares authorized | shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 600,000,000 | 600,000,000 |  |  |  |
Preferred Stock, Shares Authorized | shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20,000,000 | 20,000,000 |  |  |  |
Common Stock, Shares, Outstanding | shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 391,760,051 | 382,135,680 |  |  |  |
Preferred Stock, Shares Outstanding | shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 440,000 | 440,000 |  |  |  |
Common Stock, Dividends, Per Share, Declared | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.84 | $ 0.80 | $ 0.78 |  |  |
Shares, Issued | shares |  |  |  |  |  |  |  |  |  |  |  |  |  | 372,363,000 | 391,760,000 | 382,136,000 | 372,363,000 |  |  | 337,016,000
Common stock, par value | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.01 | $ 0.01 |  |  |  |
Proceeds from Issuance of Preferred Stock and Preference Stock | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.0 | $ 0.0 | $ 880.0 |  |  |
Preferred Stock, Par or Stated Value Per Share | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.01 | $ 0.01 |  |  |  |
Series A Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Shares Outstanding | shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 400,000 |  |  |  |  |
Preferred Stock, Shares Issued | shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 400,000 |  |  |  |  |
Preferred Stock, Dividend Rate, Percentage |  |  |  |  |  |  |  |  | 5.65% |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Liquidation Preference Per Share | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,000.00 |  |  |  |  |
Preferred Stock, Dividend Rate, Initial Margin |  |  |  |  |  |  |  |  | 2.843% |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Dividend Rate, Initial Margin Plus 1.000% |  |  |  |  |  |  |  |  | 1.00% |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Amount of Preferred Dividends in Arrears | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1.0 |  |  |  |  |
Preferred Stock, Per Share Amounts of Preferred Dividends in Arrears | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2.51 |  |  |  |  |
Preferred Stock, Liquidation Preference, Value | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 400.0 |  |  |  |  |
Series B Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Shares Outstanding | shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20,000 |  |  |  |  |
Preferred Stock, Dividend Rate, Percentage |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.50% |  |  |  |  |  |
Preferred Stock, Liquidation Preference Per Share | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 25,000.00 |  |  |  |  |
Preferred Stock, Dividend Rate, Initial Margin |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.632% |  |  |  |  |  |
Preferred Stock, Dividend Rate, Initial Margin Plus 1.000% |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.00% |  |  |  |  |  |
Preferred Stock, Amount of Preferred Dividends in Arrears | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1.4 |  |  |  |  |
Preferred Stock, Per Share Amounts of Preferred Dividends in Arrears | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 72.23 |  |  |  |  |
Preferred Stock Depositary Shares Issued | shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20,000,000 |
Preferred Stock, Liquidation Preference, Value | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 500.0 |  |  |  |  |
Depositary Stock Liquidation Preference | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 25 |  |  |  |  |
Series B-1 Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Shares Issued | shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20,000 |  |  |  |  |
Gross Proceeds | Series A Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Preferred Stock and Preference Stock | $ |  |  |  |  |  |  |  |  | $ 400.0 |  |  |  |  |  |  |  |  |  |  |
Gross Proceeds | Series B Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Preferred Stock and Preference Stock | $ |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 500.0 |  |  |  |  |  |
Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares, Issued | shares |  |  |  |  |  |  |  |  |  | 24,964,163 |  |  |  | 376,326,000 | 395,723,000 | 386,099,000 | 376,326,000 |  |  | 340,813,000
Common stock, par value | $ / shares |  |  |  |  |  |  |  |  |  | $ 0.01 |  |  |  |  |  |  |  |  |  |
Sale of Stock, Price Per Share | $ / shares |  |  |  |  |  |  |  |  |  | $ 24.28 |  |  |  |  |  |  |  |  |  |
Common Stock | Gross Proceeds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Private Placement | $ |  |  |  |  |  |  |  |  |  | $ 606.0 |  |  |  |  |  |  |  |  |  |
Common Stock | Net Proceeds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Private Placement | $ |  |  |  |  |  |  |  |  |  | $ 599.6 |  |  |  |  |  |  |  |  |  |
At The Market Program |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number Of Equity Distribution Agreements |  |  |  |  | 4 |  |  | 5 |  |  | 4 |  |  |  |  |  |  |  |  |
Common Stock Aggregate Sale Price | $ |  |  |  |  |  |  |  | $ 500.0 |  |  | $ 500.0 |  |  |  | $ 434.4 |  |  |  |  |
Derivative, Forward Price | $ / shares |  |  |  |  |  | $ 26.55 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Shares | shares |  |  |  |  |  | 4,708,098 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative, Forward Price | $ / shares | $ 22.77 |  | $ 28.83 | $ 26.01 |  |  | $ 26.43 |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value | $ | $ 64.0 |  | $ 107.1 | $ 122.5 |  |  | $ 167.7 |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Agreement 19 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative, Forward Price | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | $ 29.26 |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Shares | shares |  |  |  |  |  |  |  |  |  |  |  |  | 3,714,400 |  |  |  |  |  |  |
Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares, Issued | shares |  |  |  |  |  |  |  |  |  |  |  |  |  | 420,000 | 440,000 | 440,000 | 420,000 |  |  | 0
Preferred Stock | Series A Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Preferred Stock and Preference Stock | $ |  |  |  |  |  |  |  |  | $ 393.9 |  |  |  |  |  |  |  |  |  |  |
Preferred Stock | Net Proceeds | Series B Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Preferred Stock and Preference Stock | $ |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 486.1 |  |  |  |  |  |
Forward August 20 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative, Forward Price | $ / shares |  |  |  |  |  |  |  |  |  |  |  | $ 23.25 |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Shares | shares |  |  |  |  |  |  |  |  |  |  |  | 2,809,029 |  |  |  |  |  |  |  |
Forward September 20 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative, Forward Price | $ / shares | $ 21.82 | $ 22.28 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value | $ | $ 31.7 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Shares | shares |  | 1,452,102 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event | Series A Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Forward Contract Indexed to Issuer's Equity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Liquidation Preference Per Share | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,000 |  |

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- Definition The maximum number of shares that could be issued to net share settle a contract, if applicable. If a contract does not have a fixed or determinable maximum number of shares that may be required to be issued, disclose the fact that a potentially infinite number of shares could be issued to settle the contract. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 40 -Section 50 -Paragraph 5 -Subparagraph (b)(2) -URI http://asc.fasb.org/extlink&oid=120519210&loc=d3e90205-114008 + Details
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- Definition Aggregate amount of cumulative preferred dividends in arrears. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21488-112644 + Details
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- Definition The per share liquidation preference (or restrictions) of nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) that has a preference in involuntary liquidation considerably in excess of the par or stated value of the shares. The liquidation preference is the difference between the preference in liquidation and the par or stated values of the share. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(d)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(28)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21484-112644 + Details
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