performed excluding the impact of foreign currency fluctuations, we present period-over-period percentage changes in our revenues and certain operating expenses on a constant currency basis in addition to the historical amounts as reported. Our constant currency calculation does not take into consideration our existing hedging activities. Presenting constant currency results of operations is a non-GAAP financial measure and is not meant to be considered in isolation or as an alternative to GAAP results of operations. However, we have presented this non-GAAP financial measure to provide investors with an additional tool to evaluate our operating results. To present this information, our current and comparative prior period revenues and certain operating expenses from entities reporting in currencies other than the U.S. Dollar are converted into U.S. Dollars at constant exchange rates rather than the actual exchange rates in effect during the respective periods (i.e. average rates in effect for the three months ended March 31, 2018 are used as exchange rates for the three months ended March 31, 2019 when comparing the three months ended March 31, 2019 with the three months ended March 31, 2018).
Liquidity and Capital Resources
As of March 31, 2019, our total indebtedness was comprised of debt and financing obligations totaling $11.0 billion consisting of (a) $8,435.5 million of principal from our senior notes, (b) approximately $1,222.3 million from our finance lease liabilities, and (c) $1,365.7 million of principal from our mortgage and loans payable (gross of debt issuance cost, debt discount, plus debt premium).
We believe we have sufficient cash, coupled with anticipated cash generated from operating activities, to meet our operating requirements, including repayment of the current portion of our debt as it becomes due, payment of expenses related to our REIT integration activities, payment of regular dividends and completion of our publicly-announced expansion projects.
In March 2019, we issued and sold 2,985,575 shares of common stock in a public equity offering and received net proceeds of approximately $1,213.4 million, net of underwriting discounts, commissions and offering expenses. As of March 31, 2019, we had $1,647.7 million of cash, cash equivalents and short-term investments. In addition to our cash and investment portfolio, we have additional liquidity available to us from our $2.0 billion revolving facility and the 2018 ATM Program as described below.
As of March 31, 2019, we had 43 irrevocable letters of credit totaling $69.4 million issued and outstanding under the revolving facility. As a result, we had a total of approximately $1.9 billion of additional liquidity available to us under the revolving facility.
In December 2018, we launched the 2018 ATM Program to sell up to $750.0 million of common stock in at the market offerings. As of March 31, 2019, no shares had been sold under the 2018 ATM Program.
Besides any further financing activity we may pursue, customer collections are our primary source of cash. While we believe we have a strong customer base, and have continued to experience relatively strong collections, if the current market conditions were to deteriorate, some of our customers may have difficulty paying us and we may experience increased churn in our customer base, including reductions in their commitments to us, all of which could have a material adverse effect on our liquidity. Additionally, we may pursue additional expansion opportunities, primarily the build out of new IBX data centers, in certain of our existing markets which are at or near capacity within the next year, as well as potential acquisitions and joint ventures. While we expect to fund these plans with our existing resources, additional financing, either debt or equity, may be required, and if current market conditions were to deteriorate, we may be unable to secure additional financing or any such additional financing may only be available to us on unfavorable terms. An inability to pursue additional expansion opportunities will have a material adverse effect on our ability to maintain our desired level of revenue growth in future periods.
Sources and Uses of Cash
Three Months Ended March 31,
(dollars in thousands)
Net cash provided by operating activities
Net cash used in investing activities
Net cash provided by financing activities
Operating Activities. Cash provided by our operations is generated by colocation, interconnection, managed infrastructure and other revenues. Our primary use of cash from our operating activities includes compensation and related costs, interest payments, other general corporate expenditures and taxes. Net cash provided by operating activities increased from the three months ended March 31, 2018 to the three months ended March 31, 2019 primarily due to improved operating results offset by increases in cash paid for cost of revenues, operating expenses and income taxes.