Through the end of March, we collected about 97% of our March billings, which was in line with what we experienced before COVID-19.
For April billings, as of April 22, we have collected about 93%, which includes Pier 1.
Because we're in the early phases of experiencing the economic impact of COVID-19, it's prudent to include in our updated guidance an additional $1 million of reserves for bad debt, which Scott will walk through shortly.
Moving now to rent relief requests from our tenants, including those requests from clearly well capitalized tenants, total requests for rent relief in the form of rent deferral or abatement represented approximately 19% of our April billings.
Excluding the well capitalized tenants and only including tenants that ask for specific terms, this represents 8% of our April billings, of which approximately 85% have paid April rent.
This subset occupies an average of 48,000 square feet and represent a broad range of industries.
In our portfolio, as of April 22, we have signed 72% of our 2020 lease expirations, which is consistent with our experience in the past several years.
These signings have a cash rental rate increase of 8.4%.
Moving to dispositions, we closed on $13 million of sales in addition to the Tampa portfolio we closed in early February.
Through today, we've closed on $40 million of sales this year, on our way to meeting our 2020 sales guidance range of $125 million to $175 million.
Note that our sales guidance excludes the expected $55 million Phoenix sale in the third quarter, in which the tenant exercised its purchase option in 2019.
We are proceeding with all of our developments in process, which totaled 1.5 million square feet and a total investment of $154 million at March 31.
Of this group, only our 100,000 square foot Philadelphia development has been halted entirely due to statewide restrictions on construction deemed non-essential, although those restrictions will be lifted as of May 8, subject to forthcoming guidelines.
As a result of these delays, you will see in our supplemental Page 22 that we've adjusted some of our estimated completion dates accordingly.
In February, we were pleased to acquire Nottingham Ridge Logistics Center, a two-building development forward totaling 751,000 square feet in the Greater Baltimore industrial market, where the submarket vacancy is under 4%.
The park has I-95 frontage and is located just 12 miles north of the Port of Baltimore at the intersection of Route 43.
Today, it is 15% pre-leased, and we are seeing good interest on the remainder of the space.
Our total investment is estimated to be $82 million with an expected cash yield of 5.7%.
In the first quarter and second quarter to date, we also completed the acquisition of two buildings in the East Bay market of Northern California for a total purchase price of $14 [Phonetic] million at a weighted average yield of 5.2%.
The first property is a 39,000 square footer in Fremont, and the other is a 23,000 square foot building in Hayward.
Both are in the I-880 corridor.
The buildings are 58% occupied.
We also acquired a 24,000 square foot building in Los Angeles in the South Bay that we plan to redevelop.
The purchase price was $14.4 million.
In the first quarter, in addition to the First Park Miami land, we also acquired a 9-acre site in Southern California in the Inland Empire East for $2 million that is developable to 189,000 square feet.
On the development front, we placed in service our Ferrero build-to-suit development at PV303 totaling 644,000 square feet with a total investment of $53 million and a stabilized yield of 7.9%.
Diluted earnings per share was $0.32 versus $0.19 one year ago.
NAREIT funds from operations were $0.45 per fully diluted share compared to $0.41 per share in 1Q 2019.
This was offset by income related to the final settlement of one of our two outstanding insurance claims for damaged properties that we previously disclosed.
Excluding these items, FFO remains unchanged at $0.45 per share.
First quarter FFO also includes an approximately $800,000 non-cash write-off of a deferred rent receivable related to our lease with Pier 1 in Baltimore.
We now -- we are now assuming Pier 1 will pay rent through June and vacate the building, the impact of which I will walk through shortly when I discuss our revised 2020 FFO and portfolio guidance.
Our occupancy was strong at 97.1%, down 50 basis points from the prior quarter and down 20 basis points from a year ago.
As for leasing volume during the quarter, we commenced approximately 2.6 million square feet of leases.
459,000 square feet were new, 1.3 million were renewals, and 925,000 square feet were for developments and acquisitions with lease-up.
Tenant retention by square footage was 68.9%.
Same-store NOI growth on a cash basis, excluding termination fees, was 8.4%.
Cash rental rates were up 10.8% overall with renewals up 8.9% and new leasing 16.1%.
And on a straight-line basis, overall rental rates were up 26.5%, with renewals increasing 27.
1% and new leasing up 24.8%.
Now, moving on to the balance sheet, at March 31, our net debt plus preferred stock to EBITDA was 5.2 times.
Today, we have approximately $70 million of cash and $400 million of availability on our line of credit, for total liquidity of $470 million.
In 2020, we recently paid off a $15 million mortgage loan and have no other debt maturities in the remainder of the year.
First, we have a $200 million term loan that matures in January at an interest rate of 3.39% with a handful of banks with which we have relationships spanning many years.
Lastly, in 2021, we have $63 million of mortgage debt coming due in October that we can pay off using the availability in our line of credit if the debt capital markets are cooperative.
On uses of capital, we anticipate development spend of approximately $100 million for the remainder of 2020 and $35 million for 2021 for a total of $135 million.
These capital needs will be funded with property sales and excess cash flow after payment of our dividend, given our AFFO payout ratio, as calculated in our supplemental, of 66%, which is one of the lowest in the REIT world.
Our NAREIT FFO and FFO before one-times item guidance are both $1.73 to $1.83 per share with a midpoint of $1.78.
This is a $0.05 per share decrease compared to the midpoint of our FFO before one-times items guidance we discussed on our fourth quarter earnings call, primarily due to a decrease in forecasted NOI due to the following.
We are now assuming that Pier 1 pays rent through June 30 and vacates.
This, plus the impact of the write-off of the non-cash deferred rent receivable, is about $0.02 per share.
We have also reduced our assumption for average quarter-end occupancy by 100 basis points to a midpoint of 96.5%.
This reflects the pushback of our leasing including Pier 1, as I just discussed, and the lease-up of our remaining vacancies to the fourth quarter at First Joliet in Chicago and Building B of First Logistics Center at 78/81 in Pennsylvania.
Excluding the FFO impact of Pier 1, this change in leasing assumption represents an additional $0.02 per share.
Lastly, we are increasing our bad debt expense assumption from $500,000 per quarter to $900,000 per quarter for the remainder of the year, which is $0.01 a share.
Including the $300,000 of bad debt expense we recognized in the first quarter, our bad debt expense assumption for 2020 is now $3 million, an increase of $1 million from our prior guidance.
Other key assumptions for guidance are as follows: same-store NOI growth on a cash basis before termination fees of 2.75% to 4.25%, a decrease of 125 basis points at the midpoint due to our updated occupancy and bad debt assumptions.
Our G&A guidance remains at $31 million to $32 million.
In total, for the full year of 2020, we expect to capitalize about $0.04 per share of interest related to our developments.

Summary:
NAREIT funds from operations were $0.45 per fully diluted share compared to $0.41 per share in 1Q 2019.
This was offset by income related to the final settlement of one of our two outstanding insurance claims for damaged properties that we previously disclosed.
Excluding these items, FFO remains unchanged at $0.45 per share.
Our NAREIT FFO and FFO before one-times item guidance are both $1.73 to $1.83 per share with a midpoint of $1.78.