Equity Award, Conversion Basis, Shares

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Number of Tranches

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Number of Trustees in Board of Trustees

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- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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- Definition

Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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- Definition

Amount of additional cost recognized for award under share-based payment arrangement from occurrence of event accelerating recognition of cost.

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- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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- Definition

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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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued 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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- Definition

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

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- Definition

Agreed-upon price for the exchange of the underlying asset relating to the share-based payment award.

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- Definition

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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Number of shares authorized for issuance under share-based payment arrangement.

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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- Definition

Percentage of vesting of award under share-based payment arrangement.

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Aggregate value of stock related to Restricted Stock Awards issued during the period.

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Share-Based Compensation - Narrative (Details) $ / shares in Units, $ in Millions					3 Months Ended		6 Months Ended
	Jun. 20, 2019 USD ($) $ / shares shares	Jan. 29, 2019 $ / shares shares	Jun. 20, 2018 USD ($) shares	Jan. 29, 2018 $ / shares shares	Jun. 30, 2019 USD ($) shares	Jun. 30, 2018 USD ($) shares	Jun. 30, 2019 USD ($) tranche $ / shares shares	Jun. 30, 2018 USD ($) shares	Dec. 31, 2018 shares	Jun. 19, 2018 $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock (in shares)					121,922,120		121,922,120		121,572,155
Compensation expense, accelerated vesting due to a staffing reduction \| $					$ 0.3		$ 0.8	$ 0.4
Common shares available for issuance (in shares)					2,857,696		2,857,696
General and Administrative Expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense \| $					$ 3.7	$ 5.1	$ 7.6	$ 10.5
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period					3 years
Number of tranches \| tranche							2
Share-based compensation arrangement (in shares)							382,413	141,605
Common Stock (in shares)					382,413	141,605	382,413	141,605
Exercise price (in dollars per share) \| $ / shares				$ 37.13
Granted shares value (in dollars per share) \| $ / shares							$ 39.65
RSUs \| Vesting in three years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percent							50.00%
RSUs \| Vesting in four years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period							1 year
Vesting percent							50.00%
RSUs at target
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity awards granted (in shares)		228,128		254,615
RSUs at maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity awards granted (in shares)		568,609		634,628
LTIP Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Conversion basis (in shares)					1		1
Number of equity awards granted (in shares)	2,940		3,200
Restricted shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period					4 years
Number of equity awards granted (in shares)	23,520	112,359	25,600	125,409
Exercise price (in dollars per share) \| $ / shares				$ 29.78
Granted shares value (in dollars per share) \| $ / shares		$ 31.77
Restricted shares and time-based LTIP Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year		1 year
Number of trustees in board of trustees	9									9
Stock issued during period, value, restricted stock award, gross \| $	$ 0.1		$ 0.1
Exercise price (in dollars per share) \| $ / shares	$ 34.01									$ 31.25
Estimated future compensation expense for unvested shares \| $					$ 8.2		$ 8.2
Weighted average period over which compensation expense will be recorded							2 years 6 months
RSUs and market-based LTIP units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated future compensation expense for unvested shares \| $					$ 16.7		$ 16.7
Weighted average period over which compensation expense will be recorded							2 years 4 months 24 days
Independent Trustee \| Restricted shares and time-based LTIP Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity awards granted (in shares)	2,940		3,200
Equity Commonwealth 2015 Omnibus Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)	2,500,000