conditioning and freight elevator service during business hours, and base building cleaning) are typically provided at no additional cost, with the tenant paying additional rent only for services which exceed base building services or for services which are provided outside normal business hours.
These escalations are based on actual expenses incurred in the prior calendar year.
If the expenses in the current year are different from those in the prior year, then during the current year, the escalations will be adjusted to reflect the actual expenses for the current year.
We recognized $20.3?million, $196.2?million, and $38.7?million of rental revenue for the years ended December?31, 2017, 2016, and 2015 respectively, for the amortization of aggregate below-market leases in excess of above-market leases and a reduction in lease origination costs, resulting from the allocation of the purchase price of the applicable properties.
Included in rental revenue for the year ended December?31, 2016 is $172.4 million related to the amortization of belowmarket leases at 388-390?Greenwich Street as a result of the tenant exercising their option to purchase the property and entering into an agreement to accelerate the sale.
We recognized as a reduction to interest expense the amortization of the above-market rate mortgages assumed of $0.8?million, $2.8?million, and $2.3?million for the years ended December?31, 2017, 2016 and 2015, respectively.
The following summarizes our identified intangible assets (acquired above-market leases and in-place leases) and intangible liabilities (acquired below-market leases) as of December?31, 2017 and 2016 (in thousands):
## Table 0 ##
(1) As of December?31, 2017, $13.9 million net intangible assets and $4.1 million net intangible liabilities were reclassified to assets held for sale and liabilities related to assets held for sale.
The estimated annual amortization of acquired above-market leases, net of acquired (below-market) leases (a component of rental revenue), for each of the five succeeding years is as follows (in thousands):
## Table 1 ##
The estimated annual amortization of all other identifiable assets (a component of depreciation and amortization expense) including tenant improvements for each of the five succeeding years is as follows (in thousands): @T@We record a gain on sale of real estate when title is conveyed to the buyer, subject to the buyer’s financial commitment being sufficient to provide economic substance to the sale and provided that we have no substantial economic involvement with the?buyer.
Interest income on debt and preferred equity investments is accrued based on the contractual terms of the instruments and when, in the opinion of management, it is deemed collectible.
Some debt and preferred equity investments provide for accrual of interest at specified rates, which differ from current payment terms.
Interest is recognized on such loans at the accrual rate subject to management’s determination that accrued interest is ultimately collectible, based on the underlying collateral and operations of the borrower.
If management cannot make this determination, interest income above the current pay rate is recognized only upon actual receipt.
Deferred origination fees, original issue discounts and loan origination costs, if any, are recognized as an adjustment to interest income over the terms of the related investments using the effective interest method.
Fees received in connection with loan commitments are also deferred until the loan is funded and are then recognized over the term of the loan as an adjustment to yield.
Discounts or premiums associated with the purchase of loans are amortized or accreted into interest income as a yield adjustment on the effective interest method based on expected cash flows through the expected maturity date of the related investment.
If we purchase a debt or preferred equity investment at a discount, intend to hold it until maturity and expect to recover the full value of the investment, we accrete the discount into income as an adjustment to yield over the term of the investment.
If we purchase a debt or preferred equity investment at a discount with the intention of foreclosing on the collateral, we do not accrete the discount.
For debt investments acquired at a discount for credit quality, the difference between contractual cash flows and expected cash flows at acquisition is not accreted.
Anticipated exit fees, the collection of which is expected, are also recognized over the term of the loan as an adjustment to yield.
Debt and preferred equity investments are placed on a nonaccrual status at the earlier of the date at which payments become 90?days past due or when, in the opinion of management, a full recovery of interest income becomes doubtful.
Interest income recognition on any non-accrual debt or preferred equity investment is resumed when such non-accrual debt or preferred equity investment becomes contractually current and performance is demonstrated to be resumed.
Interest is recorded as income on impaired loans only to the extent cash is received.
Senior Unsecured Notes The following table sets forth our senior unsecured notes and other related disclosures as of December 31, 2018 and 2017, respectively, by scheduled maturity date (amounts in thousands):
## Table 2 ##
(1) Interest rate as of December 31, 2018, taking into account interest rate hedges in effect during the period.
Floating rate notes are presented with the stated spread over 3-month LIBOR, unless otherwise specified.
Interest on the senior unsecured notes is payable semi-annually with principal and unpaid interest due on the scheduled maturity dates.
(2) Issued by the Company and the Operating Partnership as co-obligors.
(3) Issued by the Operating Partnership with the Company as the guarantor.
(4) Beginning on August 8, 2019 and at any time thereafter, the notes are subject to redemption at the Company's option, in whole but not in part, at a redemption price equal to 100% of the principal amount of the notes, plus unpaid accrued interest thereon to the redemption date.
(5) In October 2017, the Company and the Operating Partnership as co-obligors issued an additional $100.0 million of 4.50% senior unsecured notes due December 2022.
The notes were priced at 105.334%.
(6) The balance was repaid in August 2018.
Restrictive Covenants The terms of the 2017 credit facility and certain of our senior unsecured notes include certain restrictions and covenants which may limit, among other things, our ability to pay dividends, make certain types of investments, incur additional indebtedness, incur liens and enter into negative pledge agreements and dispose of assets, and which require compliance with financial ratios relating to the maximum ratio of total indebtedness to total asset value, a minimum ratio of EBITDA to fixed charges, a maximum ratio of secured indebtedness to total asset value and a maximum ratio of unsecured indebtedness to unencumbered asset value.
The dividend restriction referred to above provides that, we will not during any time when a default is continuing, make distributions with respect to common stock or other equity interests, except to enable the Company to continue to qualify as a REIT for Federal income tax purposes.
As of December 31, 2018 and 2017, we were in compliance with all such covenants.
Junior Subordinated Deferrable Interest Debentures In June 2005, the Company and the Operating Partnership issued $100.0 million in unsecured trust preferred securities through a newly formed trust, SL Green Capital Trust I, or the Trust, which is a wholly-owned subsidiary of the Operating Partnership.
The securities mature in 2035 and bear interest at a floating rate of 125 basis points over the three-month LIBOR.
Interest payments may be deferred for a period of up to eight consecutive quarters if the Operating Partnership exercises its right to defer such payments.
The Trust preferred securities are redeemable at the option of the Operating Partnership, in whole or in part, with no prepayment premium.
We do not consolidate the Trust even though it is a variable interest entity as we are not the primary beneficiary.
Because the Trust is not consolidated, we have recorded the debt on our consolidated balance sheets and the related payments are classified as interest expense.
Interest Rate Risk We are exposed to changes in interest rates primarily from our variable rate debt.
Our exposure to interest rate fluctuations are managed through either the use of interest rate derivative instruments and/or through our variable rate debt and preferred equity investments.
Based on the debt outstanding as of December 31, 2018, a hypothetical 100 basis point increase in the floating rate interest rate curve would increase our consolidated annual interest cost, net of interest income from variable rate debt and preferred equity investments, by $7.1 million and would increase our share of joint venture annual interest cost by $14.3 million.
At December 31, 2018, 61.9% of our $2.1 billion debt and preferred equity portfolio is indexed to LIBOR.
We recognize most derivatives on the balance sheet at fair value.
Derivatives that are not hedges are adjusted to fair value through income.
If a derivative is considered a hedge, depending on the nature of the hedge, changes in the fair value of the derivative will either be offset against the change in fair value of the hedged asset, liability, or firm commitment through earnings, or recognized in other comprehensive income until the hedged item is recognized in earnings.
The ineffective portion of a derivative's change in fair value is immediately recognized in earnings.
Our long-term debt of $3.5 billion bears interest at fixed rates, and therefore the fair value of these instruments is affected by changes in the market interest rates.
Our variable rate debt and variable rate joint venture debt as of December 31, 2018 bore interest at rates between LIBOR plus 18 basis points and LIBOR plus 340 basis points.
Contractual Obligations The combined aggregate principal maturities of mortgages and other loans payable, the 2017 credit facility, senior unsecured notes (net of discount), trust preferred securities, our share of joint venture debt, including as-of-right extension options and put options, estimated interest expense, and our obligations under our capital lease and ground leases, as of December 31, 2018 are as follows (in thousands):
## Table 3 ##
Off-Balance Sheet Arrangements We have off-balance sheet investments, including joint ventures and debt and preferred equity investments.
These investments all have varying ownership structures.
Substantially all of our joint venture arrangements are accounted for under the equity method of accounting as we have the ability to exercise significant influence, but not control, over the operating and financial decisions of these joint venture arrangements.
Our off-balance sheet arrangements are discussed in Note 5, "Debt and Preferred Equity Investments" and Note 6, "Investments in Unconsolidated Joint Ventures" in the accompanying consolidated financial statements.
Capital Expenditures We estimate that for the year ending December 31, 2019, we expect to incur $151.1 million of recurring capital expenditures and $65.2 million of development or redevelopment expenditures on existing consolidated properties, and our share of capital expenditures at our joint venture properties will be $449.6 million.
Future property acquisitions may require substantial capital investments for refurbishment and leasing costs.
We expect to fund these capital expenditures with operating cash flow, existing liquidity, or incremental borrowings.
We expect our capital needs over the next twelve months and thereafter will be met through a combination of cash on hand, net cash provided by operations, potential asset sales, borrowings or additional equity or debt issuances.
Dividends/Distributions We expect to pay dividends to our stockholders based on the distributions we receive from our Operating Partnership primarily from property revenues net of operating expenses or, if necessary, from working capital.
To maintain our qualification as a REIT, we must pay annual dividends to our stockholders of at least 90% of our REIT taxable income, determined before taking into consideration the dividends paid deduction and net capital gains.
We intend to continue to pay regular quarterly dividends to our stockholders.
Based on our current annual dividend rate of $3.40 per share, we would pay $298.6 million in dividends to our common stockholders on an annual basis.
Before we pay any dividend, whether for
SL Green Realty Corp.  and SL Green Operating Partnership, L. P.  Notes to Consolidated Financial Statements (cont. )
December 31, 2018 60 pricing models, replacement cost, and termination cost are used to determine fair value.
All methods of assessing fair value result in a general approximation of value, and such value may never actually be realized.
In the normal course of business, we are exposed to the effect of interest rate changes and limit these risks by following established risk management policies and procedures including the use of derivatives.
To address exposure to interest rates, derivatives are used primarily to fix the rate on debt based on floating-rate indices and manage the cost of borrowing obligations.
We use a variety of conventional derivative products.
These derivatives typically include interest rate swaps, caps, collars and floors.
We expressly prohibit the use of unconventional derivative instruments and using derivative instruments for trading or speculative purposes.
Further, we have a policy of only entering into contracts with major financial institutions based upon their credit ratings and other factors.
We may employ swaps, forwards or purchased options to hedge qualifying forecasted transactions.
Gains and losses related to these transactions are deferred and recognized in net income as interest expense in the same period or periods that the underlying transaction occurs, expires or is otherwise terminated.
Hedges that are reported at fair value and presented on the balance sheet could be characterized as cash flow hedges or fair value hedges.
Interest rate caps and collars are examples of cash flow hedges.
Cash flow hedges address the risk associated with future cash flows of interest payments.
For all hedges held by us and which were deemed to be fully effective in meeting the hedging objectives established by our corporate policy governing interest rate risk management, no net gains or losses were reported in earnings.
The changes in fair value of hedge instruments are reflected in accumulated other comprehensive income.
For derivative instruments not designated as hedging instruments, the gain or loss, resulting from the change in the estimated fair value of the derivative instruments, is recognized in current earnings during the period of change.
Earnings per Share of the Company The Company presents both basic and diluted earnings per share, or EPS, using the two-class method, which is an earnings allocation formula that determines EPS for common stock and any participating securities according to dividends declared (whether paid or unpaid).
Under the two-class method, basic EPS is computed by dividing the income available to common stockholders by the weighted-average number of common stock shares outstanding for the period.
Basic EPS includes participating securities, consisting of unvested restricted stock that receive nonforfeitable dividends similar to shares of common stock.
Diluted EPS reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock, where such exercise or conversion would result in a lower EPS amount.
Diluted EPS also includes units of limited partnership interest.
The dilutive effect of stock options is reflected in the weighted average diluted outstanding shares calculation by application of the treasury stock method.
There was no dilutive effect for the exchangeable senior notes as the conversion premium was to be paid in cash.
Earnings per Unit of the Operating Partnership The Operating Partnership presents both basic and diluted earnings per unit, or EPU, using the two-class method, which is an earnings allocation formula that determines EPU for common units and any participating securities according to dividends declared (whether paid or unpaid).
Under the two-class method, basic EPU is computed by dividing the income available to common unitholders by the weighted-average number of common units outstanding for the period.
Basic EPU includes participating securities, consisting of unvested restricted units that receive nonforfeitable dividends similar to shares of common units.
Diluted EPU reflects the potential dilution that could occur if securities or other contracts to issue common units were exercised or converted into common units, where such exercise or conversion would result in a lower EPU amount.
The dilutive effect of unit options is reflected in the weighted average diluted outstanding units calculation by application of the treasury stock method.
There was no dilutive effect for the exchangeable senior notes as the conversion premium was to be paid in cash.
Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes.
Actual results could differ from those estimates.
Concentrations of Credit Risk Financial instruments that potentially subject us to concentrations of credit risk consist primarily of cash investments, debt and preferred equity investments and accounts receivable.
We place our cash investments with high quality financial institutions.
The collateral securing our debt and preferred equity investments is located in the New York metropolitan area.
See Note 5, "Debt and Preferred Equity Investments. "
SL Green Realty Corp.  and SL Green Operating Partnership, L. P.  Notes to Consolidated Financial Statements (cont. )
December 31, 2018 61 We perform ongoing credit evaluations of our tenants and require most tenants to provide security deposits or letters of credit.
Though these security deposits and letters of credit are insufficient to meet the total value of a tenant's lease obligation, they are a measure of good faith and a source of funds to offset the economic costs associated with lost revenue and the costs associated with re-tenanting a space.
The properties in our real estate portfolio are located in the New York metropolitan area.
The tenants located in our buildings operate in various industries.
Other than one tenant, Credit Suisse Securities (USA), Inc. , who accounts for 8.2% of our share of annualized cash rent, no other tenant in our portfolio accounted for more than 5.0% of our share of annualized cash rent, including our share of joint venture annualized cash rent, at December 31, 2018.
For the years ended December 31, 2018, 2017, and 2016, the following properties contributed more than 5.0% of our annualized cash rent, including our share of joint venture annualized cash rent:

<table><tr><td></td><td colspan="2">December 31,</td></tr><tr><td></td><td>2017</td><td>2016</td></tr><tr><td>Identified intangible assets (included in other assets):</td><td></td><td></td></tr><tr><td>Gross amount</td><td>$325,880</td><td>$651,099</td></tr><tr><td>Accumulated amortization</td><td>-277,038</td><td>-410,930</td></tr><tr><td>Net<sup>-1</sup></td><td>$48,842</td><td>$240,169</td></tr><tr><td>Identified intangible liabilities (included in deferred revenue):</td><td></td><td></td></tr><tr><td>Gross amount</td><td>$540,283</td><td>$655,930</td></tr><tr><td>Accumulated amortization</td><td>-402,583</td><td>-464,749</td></tr><tr><td>Net<sup>-1</sup></td><td>$137,700</td><td>$191,181</td></tr></table>
<table><tr><td>2018</td><td>$-13,853</td></tr><tr><td>2019</td><td>-13,250</td></tr><tr><td>2020</td><td>-12,432</td></tr><tr><td>2021</td><td>-3,950</td></tr><tr><td>2022</td><td>-3,647</td></tr></table>
<table><tr><td></td><td>2019</td><td>2020</td><td>2021</td><td>2022</td><td>2023</td><td>Thereafter</td><td>Total</td></tr><tr><td>Property mortgages and other loans</td><td>$6,241</td><td>$26,640</td><td>$151,505</td><td>$208,017</td><td>$122,851</td><td>$1,145,405</td><td>$1,660,659</td></tr><tr><td>MRA and FHLB facilities</td><td>27,500</td><td>300,000</td><td>—</td><td>—</td><td>—</td><td>—</td><td>327,500</td></tr><tr><td>Revolving credit facility</td><td>—</td><td>—</td><td>—</td><td>—</td><td>500,000</td><td>—</td><td>500,000</td></tr><tr><td>Unsecured term loans</td><td>—</td><td>—</td><td>—</td><td>—</td><td>1,300,000</td><td>200,000</td><td>1,500,000</td></tr><tr><td>Senior unsecured notes</td><td>—</td><td>250,000</td><td>350,000</td><td>800,000</td><td>—</td><td>100,000</td><td>1,500,000</td></tr><tr><td>Trust preferred securities</td><td>—</td><td>—</td><td>—</td><td>—</td><td>—</td><td>100,000</td><td>100,000</td></tr><tr><td>Capital lease</td><td>2,411</td><td>2,620</td><td>2,794</td><td>2,794</td><td>2,794</td><td>817,100</td><td>830,513</td></tr><tr><td>Ground leases</td><td>31,066</td><td>31,436</td><td>31,628</td><td>29,472</td><td>27,166</td><td>676,090</td><td>826,858</td></tr><tr><td>Estimated interest expense</td><td>222,554</td><td>196,142</td><td>185,017</td><td>150,712</td><td>81,781</td><td>193,794</td><td>1,030,000</td></tr><tr><td>Joint venture debt</td><td>115,295</td><td>278,791</td><td>518,371</td><td>220,810</td><td>277,996</td><td>2,430,198</td><td>3,841,461</td></tr><tr><td>Total</td><td>$405,067</td><td>$1,085,629</td><td>$1,239,315</td><td>$1,411,805</td><td>$2,312,588</td><td>$5,662,587</td><td>$12,116,991</td></tr></table>
<table><tr><td>Issuance</td><td>December 31,2018UnpaidPrincipalBalance</td><td>December 31,2018AccretedBalance</td><td>December 31,2017AccretedBalance</td><td colspan="2">Interest Rate -1</td><td>Initial Term(in Years)</td><td>Maturity Date</td></tr><tr><td>March 16, 2010<sup>-2</sup></td><td>$250,000</td><td>$250,000</td><td>$250,000</td><td></td><td>7.75%</td><td>10</td><td>March 2020</td></tr><tr><td>August 7, 2018<sup>-3 (4)</sup></td><td>350,000</td><td>350,000</td><td>—</td><td>L+</td><td>0.98%</td><td>3</td><td>August 2021</td></tr><tr><td>October 5, 2017<sup>-3</sup></td><td>500,000</td><td>499,591</td><td>499,489</td><td></td><td>3.25%</td><td>5</td><td>October 2022</td></tr><tr><td>November 15, 2012<sup>-5</sup></td><td>300,000</td><td>304,168</td><td>305,163</td><td></td><td>4.50%</td><td>10</td><td>December 2022</td></tr><tr><td>December 17, 2015<sup>-2</sup></td><td>100,000</td><td>100,000</td><td>100,000</td><td></td><td>4.27%</td><td>10</td><td>December 2025</td></tr><tr><td>August 5, 2011<sup>-2 (6)</sup></td><td>—</td><td>—</td><td>249,953</td><td></td><td></td><td></td><td></td></tr><tr><td></td><td>$1,500,000</td><td>$1,503,759</td><td>$1,404,605</td><td></td><td></td><td></td><td></td></tr><tr><td>Deferred financing costs, net</td><td></td><td>-8,545</td><td>-8,666</td><td></td><td></td><td></td><td></td></tr><tr><td></td><td>$1,500,000</td><td>$1,495,214</td><td>$1,395,939</td><td></td><td></td><td></td><td></td></tr></table>

Question: what's the total amount of Gross amount of December 31, 2017, and December 17, 2015 of December 31,2018UnpaidPrincipalBalance ?
Answer: 425880