NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS – (Continued)
The fair value of property, plant and equipment was estimated by applying the cost approach, with the exception of land which was estimated by applying the market approach, for the Metronode Acquisition. For the Infomart Dallas Acquisition, the fair values of land, building and personal property were estimated by applying the market approach, residual income method and cost approach, respectively. The cost approach uses the replacement or reproduction cost as an indicator of fair value. The premise of the cost approach is that a market participant would pay no more for an asset than the amount for which the asset could be replaced or reproduced. The key assumptions of the cost approach include replacement cost new, physical deterioration, functional and economic obsolescence, economic useful life, remaining useful life, age and effective age. The residual income method estimates the fair value of the Infomart Dallas building using an income approach less the fair values attributed to land, personal property, in-place leases and favorable and unfavorable leases.
Goodwill represents the excess of the purchase price over the fair value of the net tangible and intangible assets acquired and liabilities assumed. Goodwill is attributable to the workforce of the acquired business and the projected revenue increase expected to arise from future customers after the Metronode and Infomart Dallas acquisitions. Goodwill from the acquisition of Metronode is not amortizable for local tax purposes and is attributable to the Company's Asia-Pacific region. Goodwill from the acquisition of Infomart Dallas is deductible for local tax purposes and is attributable to the Company's Americas region. Operating results of Metronode and Infomart Dallas have been reported in the Asia-Pacific and Americas regions, respectively.
For the three months ended March 31, 2019, the Company's results of operations include $27.2 million of revenues and insignificant net income from operations from the combined operations of Metronode and Infomart Dallas.
Derivatives and Hedging Activities
Derivatives Designated as Hedging Instruments
Net Investment Hedges. The Company is exposed to the impact of foreign exchange rate fluctuations on the value of investments in its foreign subsidiaries whose functional currencies are other than the U.S. Dollar. In order to mitigate the impact of foreign currency exchange rates, the Company has entered into various foreign currency debt obligations, which are designated as hedges against the Company's net investments in foreign subsidiaries. As of March 31, 2019 and December 31, 2018, the total principal amounts of foreign currency debt obligations designated as net investment hedges were $4,113.0 million and $4,139.8 million, respectively.
The Company also uses cross-currency interest rate swaps to hedge a portion of its net investment in its European operations. As of March 31, 2019, U.S. Dollar to Euro cross-currency interest rate swap contracts with a total notional amount of $750.0 million were outstanding, with maturity dates in April 2022, January 2024 and January 2025. At maturity of each outstanding contract, the Company will receive U.S. Dollars from and pay Euros to the contract counterparty. During the term of each contract, the Company receives interest payments in U.S. Dollars and makes interest payments in Euros based on a notional amount and fixed interest rates determined at contract inception. The Company did not have any cross-currency interest rate swaps outstanding as of December 31, 2018.