Number of common stock shares to which each Preferred share is convertible after special dividend.

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Price of a single share of a number of repurchase stocks of a company.

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other Than Options, Grants in Period Net of Forfeitures

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Shares Reserved For Issuance Under Stock Purchase Plan

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Aggregate number of common shares reserved for future issuance.

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Aggregate dividends declared during the period for each share of common stock outstanding.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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The cash outflow to reacquire common stock during the period.

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Aggregate dividends declared during the period for each share of preferred stock outstanding.

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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.

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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

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Value of all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by shareholders, which is net of related treasury stock. May be all or a portion of the number of preferred shares authorized. These shares represent the ownership interest of the preferred shareholders.

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The cash inflow associated with the amount received from entity's first offering of stock to the public.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Price of a single share of a number of saleable stocks of a company.

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The number of shares issued during the period upon the conversion of units. An example of a convertible unit is an umbrella partnership real estate investment trust unit (UPREIT unit).

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Number of shares issued during the period from a dividend reinvestment plan (DRIP). A dividend reinvestment plan allows the shareholders to reinvest dividends paid to them by the entity on new issues of stock by the entity.

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Number of new stock issued during the period.

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Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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STOCKHOLDERS’ EQUITY - Other information (Details)	12 Months Ended
STOCKHOLDERS’ EQUITY - Other information (Details)	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 $ / shares shares	Dec. 31, 2008 shares
Stockholders' equity
Common stock, shares authorized	350,000,000	350,000,000
Preferred stock, shares authorized	50,000,000	50,000,000
Total consideration \| $	$ 19,988,000
Common distributions declared per share \| $ / shares	$ 1.2900	$ 1.2400	$ 1.1800
Stock issued during period, shares, Distribution Reinvestment and Stock Purchase Plan				9,957,233
Shares reserved for issuance under the Stock Purchase Plan	10,963,730
Equity Distribution Agreement
Stockholders' equity
Common stock, shares authorized	20,000,000
Common Stock, Capital Shares Reserved for Future Issuance	13,078,931
8.00% Series E Cumulative Convertible Preferred Stock
Stockholders' equity
Preferred stock, liquidation preference per share \| $ / shares	$ 16.61
Number of common stock shares to which each preferred share is convertible after special dividend	1.083
Declared preferred stock dividend \| $ / shares	$ 1.40	$ 1.33	$ 1.33
Preferred Stock, Shares Issued	2,780,994	2,780,994
Common Stock
Stockholders' equity
Issuance of common shares through public offering	7,150,000		5,000,000
Share Price \| $ / shares	$ 41.98
Aggregate gross proceeds of common stock \| $	$ 300,200,000
Repurchase of common shares	(593,373)
Average price \| $ / shares	33.69
Adjustment for conversion of non-controlling interest of unitholders			255,607
Series F
Stockholders' equity
Preferred stock, shares authorized	20,000,000
Share Price \| $ / shares	$ 0.0001
Preferred stock, value, issued \| $	$ 1,580	$ 1,585
Preferred Stock, Shares Issued	15,802,393	15,852,721
Restricted Stock
Stockholders' equity
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	212,358
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	8,208
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other Than Options, Grants in Period Net of Forfeitures	212,411