NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS – (Continued)
Fair Value of Debt Instruments
The following table sets forth the estimated fair values of the Company's mortgage and loans payable and senior notes, including current maturities, as of (in thousands):
December 31, 2017
Mortgage and loans payable
The fair value of the mortgage and loans payable, which were not publicly traded, was estimated by considering the Company's credit rating, current rates available to the Company for debt of the same remaining maturities and terms of the debt (Level 2). The fair value of the senior notes, which were traded in the public debt market, was based on quoted market prices (Level 1).
The following table sets forth total interest costs incurred and total interest costs capitalized for the periods presented (in thousands):
Three Months Ended
Nine Months Ended
Interest charges incurred
Total interest paid, net of capitalized interest, during the three months ended September 30, 2018 and 2017 was $146.7 million and $122.8 million, respectively. Total interest paid, net of capitalized interest, during the nine months ended September 30, 2018 and 2017 was $362.0 million and $321.8 million, respectively.
Commitments and Contingencies
As a result of the Company's various IBX data center expansion projects, as of September 30, 2018, the Company was contractually committed for approximately $0.8 billion of unaccrued capital expenditures, primarily for IBX infrastructure equipment not yet delivered and labor not yet provided, in connection with the work necessary to open these IBX data centers and make them available to customers for installation. The Company also had numerous other, non-capital purchase commitments in place as of September 30, 2018, such as commitments to purchase power in select locations through the remainder of 2018 and thereafter, and other open purchase orders for goods or services to be delivered or provided during the remainder of 2018 and thereafter. Such other miscellaneous purchase commitments totaled approximately $0.8 billion as of September 30, 2018. In addition, the Company entered into lease agreements in various locations for a total lease commitment of approximately $230.2 million, excluding potential lease renewals. These lease agreements will commence between April 2019 and August 2019 with lease terms of 10 to 30 years.
The Company estimates exposure on certain liabilities, such as indirect and property taxes, based on the best information available at the time of determination. With respect to real and personal property taxes, the Company records what it can reasonably estimate based on prior payment history, assessed value by the assessor's office, current landlord estimates or estimates based on current or changing fixed asset values in each specific municipality, as applicable. However, there are circumstances beyond the Company’s control whereby the underlying value of the property or basis for which the tax is calculated on the property may change, such as a landlord selling the underlying property of one of the Company’s IBX data center leases or a municipality changing the assessment value in a jurisdiction and, as a result, the Company’s property tax obligations may vary from period to period. Based upon the most current facts and circumstances, the Company makes the necessary property tax accruals for each of