| Pay vs Performance Disclosure number in Thousands | 12 Months Ended |
| Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) |
| Pay vs Performance Disclosure [Table] | | | |
| Pay vs Performance [Table Text Block] | Jordan L. Kaplan Value of Initial Fixed $100 Investment Based on: Year Summary Compensation Table Total for PEO (1) Compensation Actually Paid to PEO (2) Average Summary Compensation Table Total for Non-PEO NEOs Average Compensation Actually Paid to Non-PEO NEOs (2) Our TSR Our Peer Group TSR (3) Net Income (4) (000's) FFO 2022 $ 8,653,835 $ 4,400,000 $ 3,246,971 $ 1,539,986 $40 $63 $ 96,540 $ 419,683 2021 $ 9,071,244 $ 12,461,572 $ 3,241,910 $ 4,402,571 $82 $101 $ 56,131 $ 383,456 2020 $ 8,468,019 $ 4,965,617 $ 3,061,873 $ 1,814,463 $69 $88 $ 38,553 $ 372,541 | | |
| Company Selected Measure Name | FFO | | |
| Named Executive Officers, Footnote [Text Block] | The amounts reported are equal to the amounts reported in the "total" column of the Summary Compensation Table for the applicable year for Mr. Kaplan, and the average of the amount reported in the "total" column of the Summary Compensation Table for the Non-PEO NEOs for each applicable year. | | |
| Peer Group Issuers, Footnote [Text Block] | For each of 2022, 2021 and 2020, the following companies were included in our Peer Group: Alexandria Real Estate Equities, Inc (ARE) Boston Properties, Inc. (BXP) Empire State Realty Trust, Inc. (ESRT) Hudson Pacific Properties, Inc. (HPP) Kilroy Realty Corporation (KRC) Paramount Group, Inc. (PGRE) Piedmont Office Realty Trust, Inc. (PDM) SL Green Realty Corp. (SLG) UDR, Inc. (UDR) Vornado Realty Trust (VNO) _________________________________________________ For 2020, our Peer Group also included Digital Realty Trust, Inc. (DLR) For 2021 and 2022, our Peer Group also included JBG SMITH Properties, Inc. (JBGS) We replaced DLR with JBGS Peers in 2021 because DLR is no longer a comparable peer due to its size and global scope of operations, while JBGS is a diversified REIT that operates primarily in and around the high-barrier to entry Washington, DC market. Using DLR instead of JBGS, our peer group TSR in 2021 and 2022 would have been $69 and $113, respectively. Our Compensation Committee’s peer group also included Apartment Investment and Management Company (AIV), and Columbia Property Trust (CXP) in 2020, and Apartment Income REIT Corp (AIRC) in 2021 and 2022. These peers were excluded from our TSR peer group because they became public or delisted during the three years presented, and we therefore did not have sufficient data for the TSR calculations. | | |
| PEO Total Compensation Amount | $ 8,653,835 | $ 9,071,244 | $ 8,468,019 |
| PEO Actually Paid Compensation Amount | $ 4,400,000 | 12,461,572 | 4,965,617 |
| Adjustment To PEO Compensation, Footnote [Text Block] | Summary Compen-sation Table (SCT) Total Deduct: Stock Based Compen-sation as reported in the SCT Add: Fair Value of Award Granted that was Unvested at Year End (Measured at Year End)* Add: Fair Value of Award Granted that Vested (Measured at Vesting Date)* Add: Change in Fair Value of Prior Year Unvested Awards (Measured at Year End* Add: Change in Fair Value of Prior Year Awards that Vested (Measured at Vesting Date)* Add: Dividends Paid on Unvested Awards Prior to Vesting Date Compen-sation Actually Paid Jordan L. Kaplan 2022 $ 8,653,835 $ (7,837,901) $ 7,688,007 $ — $ (4,726,489) $ 45,475 $ 577,073 $ 4,400,000 2021 $ 9,071,244 $ (8,258,608) $ 8,206,116 $ — $ 1,244,003 $ 1,659,228 $ 539,589 $ 12,461,572 2020 $ 8,468,019 $ (7,583,722) $ 7,664,775 $ — $ (3,160,261) $ (846,234) $ 423,040 $ 4,965,617 Other NEOs (Average) 2022 $ 3,246,971 $ (2,663,668) $ 2,612,727 $ — $ (1,721,125) $ (146,493) $ 211,572 $ 1,539,986 2021 $ 3,241,910 $ (2,716,419) $ 2,699,154 $ — $ 463,758 $ 519,056 $ 195,113 $ 4,402,571 2020 $ 3,061,873 $ (2,521,592) $ 2,548,542 $ — $ (1,091,981) $ (332,010) $ 149,630 $ 1,814,463 __________________________________________________________________________ *In determining CAP, grants are considered vested when the required service period is completed and the stock performance hurdle has been achieved. | | |
| Non-PEO NEO Average Total Compensation Amount | $ 3,246,971 | 3,241,910 | 3,061,873 |
| Non-PEO NEO Average Compensation Actually Paid Amount | $ 1,539,986 | 4,402,571 | 1,814,463 |
| Adjustment to Non-PEO NEO Compensation Footnote [Text Block] | Summary Compen-sation Table (SCT) Total Deduct: Stock Based Compen-sation as reported in the SCT Add: Fair Value of Award Granted that was Unvested at Year End (Measured at Year End)* Add: Fair Value of Award Granted that Vested (Measured at Vesting Date)* Add: Change in Fair Value of Prior Year Unvested Awards (Measured at Year End* Add: Change in Fair Value of Prior Year Awards that Vested (Measured at Vesting Date)* Add: Dividends Paid on Unvested Awards Prior to Vesting Date Compen-sation Actually Paid Jordan L. Kaplan 2022 $ 8,653,835 $ (7,837,901) $ 7,688,007 $ — $ (4,726,489) $ 45,475 $ 577,073 $ 4,400,000 2021 $ 9,071,244 $ (8,258,608) $ 8,206,116 $ — $ 1,244,003 $ 1,659,228 $ 539,589 $ 12,461,572 2020 $ 8,468,019 $ (7,583,722) $ 7,664,775 $ — $ (3,160,261) $ (846,234) $ 423,040 $ 4,965,617 Other NEOs (Average) 2022 $ 3,246,971 $ (2,663,668) $ 2,612,727 $ — $ (1,721,125) $ (146,493) $ 211,572 $ 1,539,986 2021 $ 3,241,910 $ (2,716,419) $ 2,699,154 $ — $ 463,758 $ 519,056 $ 195,113 $ 4,402,571 2020 $ 3,061,873 $ (2,521,592) $ 2,548,542 $ — $ (1,091,981) $ (332,010) $ 149,630 $ 1,814,463 __________________________________________________________________________ *In determining CAP, grants are considered vested when the required service period is completed and the stock performance hurdle has been achieved. | | |
| Compensation Actually Paid vs. Total Shareholder Return [Text Block] | CAP TSR | | |
| Compensation Actually Paid vs. Net Income [Text Block] | CAP Net Income (in millions) | | |
| Compensation Actually Paid vs. Company Selected Measure [Text Block] | CAP FFO | | |
| Total Shareholder Return Vs Peer Group [Text Block] | CAP TSR | | |
| Tabular List [Table Text Block] | Financial Performance Measures Total Shareholder Return ("TSR") Total Shareholder Return ("TSR") is the cumulative total shareholder return based on a $100 investment on December 31, 2019, assuming the reinvestment of dividends. For purposes of calculating TSR for our Peer Group, it is weighted according to the respective issuers' stock market capitalization at the beginning of each period presented. FFO We have chosen FFO as the "Company Selected Measure" in accordance with Item 402(v) of Regulation S-K. We calculate FFO in accordance with the standards established by NAREIT by excluding gains (or losses) on sales of investments in real estate, gains (or losses) from changes in control of investments in real estate, real estate depreciation and amortization (other than amortization of right-of-use assets for which we are the lessee and amortization of deferred loan costs), and impairment write-downs of real estate from our net income (loss) (including adjusting for the effect of such items attributable to our consolidated JVs and our unconsolidated Fund, but not for noncontrolling interests included in our calculation of fully diluted equity). We report FFO because it is a widely reported measure of the performance of equity REITs and is also used by some investors to identify the impact of trends in occupancy rates, rental rates and operating costs from year to year, excluding impacts from changes in the value of our real estate, and to compare our performance with other REITs. FFO is a non-GAAP financial measure for which we believe that net income (loss) is the most directly comparable GAAP financial measure. FFO has limitations as a measure of our performance because it excludes depreciation and amortization of real estate and captures neither the changes in the value of our properties that result from use or market conditions, nor the level of capital expenditures, tenant improvements and leasing expenses necessary to maintain the operating performance of our properties, all of which have real economic effect and could materially impact our results from operations. FFO should be considered only as a supplement to net income (loss) as a measure of our performance and should not be used as a measure of our liquidity or cash flow, nor is it indicative of funds available to fund our cash needs, including our ability to pay dividends. Other REITs may not calculate FFO in accordance with the NAREIT definition and, accordingly, our FFO may not be comparable to the FFO of other REITs. For the reconciliations of our 2022 and 2021 FFO to Net Income, see Item 7 of Part II in our 2022 Form 10-K filed with the SEC on February 17, 2023. For the reconciliation of our 2020 FFO to Net Income, see Item 7 of Part II in our 2021 Form 10-K filed with the SEC on February 18, 2022. | | |
| Total Shareholder Return Amount | $ 40 | 82 | 69 |
| Peer Group Total Shareholder Return Amount | 63 | 101 | 88 |
| Net Income (Loss) | $ 96,540,000 | $ 56,131,000 | $ 38,553,000 |
| Company Selected Measure Amount | 419,683 | 383,456 | 372,541 |
| PEO Name | Mr. Kaplan | | |
| Additional 402(v) Disclosure [Text Block] | As described in greater detail in the section of this Proxy Statement entitled "Compensation Discussion and Analysis," our executive compensation philosophy emphasizes incentive-based compensation, evaluated over a variety of factors. In accordance with Item 402(v) of Regulation S-K, the most important financial performance measures that we use to link compensation for the named executive officers, for the most recently completed fiscal year, to the Company’s performance are as follows:As required by Section 953(a) of the Dodd-Frank Wall Street Reform and Consumer Protection Act, and item 402(v) of Regulation S-K, we are providing the following information about the relationship between the amount of CAP to our named executive officers and certain measures of our financial performance. For further information concerning our performance-focused compensation philosophy and how the Compensation Committee considers performance in relation to compensation decisions, refer to the "Compensation Discussion and Analysis" section of this proxy statement. The tabular and narrative disclosures provided below, calculated in accordance with the applicable rules, may reflect reasonable estimates and assumptions. The table below presents the compensation information for our principal executive officer (PEO) and, as an average, for our other named executive officers (the "Non-PEO NEOs") and the financial performance information as required by the SEC’s pay versus performance for 2022, 2021 and 2020. Our PEO, Mr. Kaplan, and our Non-PEO NEOs, Messrs., Emmett, Panzer, Crummy and Seymour, were the same during 2022, 2021 and 2020.The amounts reported represent Mr. Kaplan's CAP amount, and the average CAP amount for the Non-PEO NEOs, for the corresponding fiscal year, as computed in accordance with Item 402(v) of Regulation S-K and as further described below. The dollar amounts do not reflect the actual amount of compensation earned by or paid to Mr. Kaplan, or any of the Non-PEO NEOs during the applicable year. In accordance with the requirements of Item 402(v) of Regulation S-K, the table below sets forth the adjustments that were made to Mr. Kaplan's, and to the Non-PEO NEOs, total compensation for each year to determine the CAP amounts. There were no grants forfeited by our NEOs during 2022; therefore, no adjustments have been made to the Summary Compensation Table totals for forfeitures. The Company does not sponsor or maintain a defined benefit pension plan, and no such benefits are provided to our NEOs; therefore, no adjustments have been made to the Summary Compensation Table totals for changes in pension values.The amounts reported represent our net income attributable to our common stockholders, as reflected in our audited financial statements in our Form 10-K for the applicable year.In accordance with Item 402(v) of Regulation S-K, we are providing the graphs below to illustrate the relationships between the reported CAP amounts and each of the financial performance measures presented in the Pay Versus Performance Table. As described more fully in the "Compensation Discussion and Analysis" section of this Proxy Statement, the Compensation Committee make compensation decisions based on a number of factors, and has not, specifically evaluated the relationship between the performance measures reported in the Pay Versus Performance Table with the named executive officers' CAP amounts (as calculated in accordance with Item 402(v) of Regulation S-K) for a particular year. Therefore, the alignment outcomes depicted below below may not accurately reflect the Compensation Committee's goals of linking pay with performance and aligning the interests of our named executive officers with those of our stockholders. | | |
| Measure [Axis]: 1 | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Measure Name | Total Shareholder Return ("TSR") | | |
| Non-GAAP Measure Description [Text Block] | Total Shareholder Return ("TSR") is the cumulative total shareholder return based on a $100 investment on December 31, 2019, assuming the reinvestment of dividends. For purposes of calculating TSR for our Peer Group, it is weighted according to the respective issuers' stock market capitalization at the beginning of each period presented. | | |
| Measure [Axis]: 2 | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Measure Name | FFO | | |
| Non-GAAP Measure Description [Text Block] | We have chosen FFO as the "Company Selected Measure" in accordance with Item 402(v) of Regulation S-K. We calculate FFO in accordance with the standards established by NAREIT by excluding gains (or losses) on sales of investments in real estate, gains (or losses) from changes in control of investments in real estate, real estate depreciation and amortization (other than amortization of right-of-use assets for which we are the lessee and amortization of deferred loan costs), and impairment write-downs of real estate from our net income (loss) (including adjusting for the effect of such items attributable to our consolidated JVs and our unconsolidated Fund, but not for noncontrolling interests included in our calculation of fully diluted equity). We report FFO because it is a widely reported measure of the performance of equity REITs and is also used by some investors to identify the impact of trends in occupancy rates, rental rates and operating costs from year to year, excluding impacts from changes in the value of our real estate, and to compare our performance with other REITs. FFO is a non-GAAP financial measure for which we believe that net income (loss) is the most directly comparable GAAP financial measure. FFO has limitations as a measure of our performance because it excludes depreciation and amortization of real estate and captures neither the changes in the value of our properties that result from use or market conditions, nor the level of capital expenditures, tenant improvements and leasing expenses necessary to maintain the operating performance of our properties, all of which have real economic effect and could materially impact our results from operations. FFO should be considered only as a supplement to net income (loss) as a measure of our performance and should not be used as a measure of our liquidity or cash flow, nor is it indicative of funds available to fund our cash needs, including our ability to pay dividends. Other REITs may not calculate FFO in accordance with the NAREIT definition and, accordingly, our FFO may not be comparable to the FFO of other REITs. For the reconciliations of our 2022 and 2021 FFO to Net Income, see Item 7 of Part II in our 2022 Form 10-K filed with the SEC on February 17, 2023. For the reconciliation of our 2020 FFO to Net Income, see Item 7 of Part II in our 2021 Form 10-K filed with the SEC on February 18, 2022. | | |
| PEO [Member] | Stock Awards Adjustment [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | $ (7,837,901) | $ (8,258,608) | $ (7,583,722) |
| PEO [Member] | Equity Awards Granted During the Year, Unvested [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 7,688,007 | 8,206,116 | 7,664,775 |
| PEO [Member] | Equity Awards Granted During the Year, Vested [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 0 | 0 | 0 |
| PEO [Member] | Equity Awards Granted in Prior Years, Unvested [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | (4,726,489) | 1,244,003 | (3,160,261) |
| PEO [Member] | Equity Awards Granted in Prior Years, Vested [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 45,475 | 1,659,228 | (846,234) |
| PEO [Member] | Equity Awards, Value of Dividends and Other Earnings Paid Adjustment [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 577,073 | 539,589 | 423,040 |
| Non-PEO NEO [Member] | Stock Awards Adjustment [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | (2,663,668) | (2,716,419) | (2,521,592) |
| Non-PEO NEO [Member] | Equity Awards Granted During the Year, Unvested [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 2,612,727 | 2,699,154 | 2,548,542 |
| Non-PEO NEO [Member] | Equity Awards Granted During the Year, Vested [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 0 | 0 | 0 |
| Non-PEO NEO [Member] | Equity Awards Granted in Prior Years, Unvested [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | (1,721,125) | 463,758 | (1,091,981) |
| Non-PEO NEO [Member] | Equity Awards Granted in Prior Years, Vested [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | (146,493) | 519,056 | (332,010) |
| Non-PEO NEO [Member] | Equity Awards, Value of Dividends and Other Earnings Paid Adjustment [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | $ 211,572 | $ 195,113 | $ 149,630 |
