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Secured and unsecured senior debt (Notes)
 12 Months Ended
Dec. 31, 2024
Debt Disclosure [Abstract]  
Secured and unsecured senior debt The following table summarizes our outstanding indebtedness and respective principal payments remaining as of December 31, 2024 (dollars in thousands):
Stated 
Rate
Interest
Rate(1)
Maturity
Date(2)
Principal Payments Remaining for the Periods Ending December 31,
Unamortized
(Deferred
Financing
Cost),
(Discount)
Premium
Debt
2025
2026
2027
2028
2029
Thereafter
Principal
Total
Secured notes payable
Greater Boston(3)
SOFR+2.70%
7.52%
11/19/26
$—
$149,594
$—
$—
$—
$—
$149,594
$(272)
$149,322
San Francisco Bay Area
6.50%
6.50
7/1/36
34
36
38
41
44
394
587
—
587
Secured debt weighted-average interest
rate/subtotal
7.51
34
149,630
38
41
44
394
150,181
(272)
149,909
Unsecured senior line of credit and
commercial paper program(4)
(4)
N/A
(4)
1/22/30
(4)
—
—
—
—
—
—
—
—
—
Unsecured senior notes payable
3.45%
3.62
4/30/25
600,000
—
—
—
—
—
600,000
(296)
599,704
Unsecured senior notes payable
4.30%
4.50
1/15/26
—
300,000
—
—
—
—
300,000
(532)
299,468
Unsecured senior notes payable
3.80%
3.96
4/15/26
—
350,000
—
—
—
—
350,000
(653)
349,347
Unsecured senior notes payable
3.95%
4.13
1/15/27
—
—
350,000
—
—
—
350,000
(1,067)
348,933
Unsecured senior notes payable
3.95%
4.07
1/15/28
—
—
—
425,000
—
—
425,000
(1,312)
423,688
Unsecured senior notes payable
4.50%
4.60
7/30/29
—
—
—
—
300,000
—
300,000
(1,027)
298,973
Unsecured senior notes payable
2.75%
2.87
12/15/29
—
—
—
—
400,000
—
400,000
(2,064)
397,936
Unsecured senior notes payable
4.70%
4.81
7/1/30
—
—
—
—
—
450,000
450,000
(2,057)
447,943
Unsecured senior notes payable
4.90%
5.05
12/15/30
—
—
—
—
—
700,000
700,000
(4,730)
695,270
Unsecured senior notes payable
3.375%
3.48
8/15/31
—
—
—
—
—
750,000
750,000
(4,348)
745,652
Unsecured senior notes payable
2.00%
2.12
5/18/32
—
—
—
—
—
900,000
900,000
(6,967)
893,033
Unsecured senior notes payable
1.875%
1.97
2/1/33
—
—
—
—
—
1,000,000
1,000,000
(7,109)
992,891
Unsecured senior notes payable
2.95%
3.07
3/15/34
—
—
—
—
—
800,000
800,000
(7,236)
792,764
Unsecured senior notes payable
4.75%
4.88
4/15/35
—
—
—
—
—
500,000
500,000
(4,958)
495,042
Unsecured senior notes payable
5.25%
5.38
5/15/36
—
—
—
—
—
400,000
400,000
(4,109)
395,891
Unsecured senior notes payable
4.85%
4.93
4/15/49
—
—
—
—
—
300,000
300,000
(2,872)
297,128
Unsecured senior notes payable
4.00%
3.91
2/1/50
—
—
—
—
—
700,000
700,000
9,985
709,985
Unsecured senior notes payable
3.00%
3.08
5/18/51
—
—
—
—
—
850,000
850,000
(11,227)
838,773
Unsecured senior notes payable
3.55%
3.63
3/15/52
—
—
—
—
—
1,000,000
1,000,000
(13,673)
986,327
Unsecured senior notes payable
5.15%
5.26
4/15/53
—
—
—
—
—
500,000
500,000
(7,592)
492,408
Unsecured senior notes payable
5.625%
5.71
5/15/54
—
—
—
—
—
600,000
600,000
(6,691)
593,309
Unsecured debt weighted-average interest
rate/subtotal
3.81
600,000
650,000
350,000
425,000
700,000
9,450,000
12,175,000
(80,535)
12,094,465
Weighted-average interest rate/total
3.86%
$600,034
$799,630
$350,038
$425,041
$700,044
$9,450,394
$12,325,181
$(80,807)
$12,244,374
(1)Represents the weighted-average interest rate as of the end of the applicable period, including amortization of loan fees, amortization of debt premiums (discounts), and other bank fees.
(2)Reflects any extension options that we control.
(3)Represents a secured construction loan held by our consolidated real estate joint venture for 99 Coolidge Avenue, of which we own a 75.0% interest. As of December 31, 2024, this joint venture has $45.7 million available under existing
lender commitments. The interest rate shall be reduced from SOFR+2.70% to SOFR+2.10% over time upon the completion of certain leasing, construction, and financial covenant milestones. During the three months ended December 31,
2024, we extended the maturity date for a secured construction loan held by our consolidated real estate joint venture at 99 Coolidge Avenue to November 19, 2025. We have a one-year option to extend the maturity date to November 19,
2026, subject to certain conditions.
(4)Refer to “$5.0 billion unsecured senior line of credit” and “$2.5 billion commercial paper program” on the following page.
The following table summarizes our secured and unsecured senior debt and amounts outstanding under our unsecured senior
line of credit and commercial paper program as of December 31, 2024 (dollars in thousands):
Fixed-Rate
Debt
Variable-Rate
Debt
Weighted-Average
Interest
Remaining
Term
(in years)
Total
Percentage
Rate(1)
Secured notes payable
$587
$149,322
$149,909
1.2%
7.51%
1.9
Unsecured senior notes payable
12,094,465
—
12,094,465
98.8
3.81
12.8
Unsecured senior line of credit
and commercial paper program
—
—
—
(2)
—
N/A
(2)
5.1
(3)
Total/weighted average
$12,095,052
$149,322
$12,244,374
100.0%
3.86%
12.7
(3)
Percentage of total debt
98.8%
1.2%
100%
(1)Represents the weighted-average interest rate as of the end of the applicable period, including expense/income related to the amortization of loan fees, amortization of
debt premiums (discounts), and other bank fees.
(2)As of December 31, 2024, we had no outstanding balance on our unsecured senior line of credit and no commercial paper notes outstanding.
(3)We calculate the weighted-average remaining term of our commercial paper notes by using the maturity date of our unsecured senior line of credit. Using the maturity
date of our outstanding commercial paper notes, the consolidated weighted-average maturity of our debt is 12.7 years. The commercial paper notes sold during the year
ended December 31, 2024 were issued at a weighted-average yield to maturity of 5.30% and had a weighted-average maturity term of 18 days.
Unsecured senior notes payable
In February 2024, we issued $1.0 billion of unsecured senior notes payable with a weighted-average interest rate of 5.48%
and a weighted-average maturity of 23.1 years. The unsecured senior notes consisted of $400.0 million of 5.25% unsecured senior
notes due 2036 and $600.0 million of 5.625% unsecured senior notes due 2054.
$5.0 billion unsecured senior line of credit
As of December 31, 2024, our unsecured senior line of credit had aggregate commitments of $5.0 billion and bore an interest
rate of SOFR plus 0.855%. In addition to the cost of borrowing, the unsecured senior line of credit is subject to an annual facility fee of
0.145% based on the aggregate commitments outstanding. Based upon our ability to achieve certain annual sustainability metrics, the
interest rate and facility fee rate are also subject to upward or downward adjustments of up to four basis points with respect to the
interest rate and up to one basis point with respect to the facility fee rate.
Based on certain sustainability metrics achieved in accordance with the terms of our unsecured senior line of credit
agreement, the borrowing rate was reduced for a one-year period by two basis points to SOFR plus 0.855%, from SOFR plus 0.875%,
and the facility fee was reduced by 0.5 basis point to 0.145% from 0.15%. As of December 31, 2024, we had no outstanding balance on
our unsecured line of credit.
In September 2024, we amended and restated our unsecured senior line of credit to, among other changes, extend the
maturity date from January 22, 2028 to January 22, 2030, including extension options that we control.
$2.5 billion commercial paper program
Our commercial paper program provides us with the ability to issue up to $2.5 billion of commercial paper notes that bear
interest at short-term fixed rates with a maturity of generally 30 days or less and a maximum maturity of 397 days from the date of
issuance. Our commercial paper program is backed by our unsecured senior line of credit, and at all times we expect to retain a
minimum undrawn amount of borrowing capacity under our unsecured senior line of credit equal to any outstanding notes issued under
our commercial paper program. We use the net proceeds from the issuances of the notes for general working capital and other general
corporate purposes. General corporate purposes may include, but are not limited to, the repayment of other debt and selective
development, redevelopment, or acquisition of properties. During the year ended December 31, 2024, the commercial paper notes were
issued at a weighted-average yield to maturity of 5.30% and had a weighted-average maturity term of 18 days. As of December 31,
2024, we had no outstanding balance on our commercial paper program.
Interest expense
The following table summarizes interest expense for the years ended December 31, 2024, 2023, and 2022 (in thousands):
Year Ended December 31,
2024
2023
2022
Interest incurred
$516,799
$438,182
$372,848
Capitalized interest
(330,961)
(363,978)
(278,645)
Interest expense
$185,838
$74,204
$94,203