training, and the make-up of both existing backlog as well as new business being pursued, in terms of project size, technical application and facility type, end-use customers and industries, and location of the work.
Most of our operations compete on a local or regional basis. Attracting and retaining effective operating unit managers is an important factor in our business, particularly in view of the relative uniqueness of each market and operation, the importance of relationships with customers and other market participants such as architects and consulting engineers, and the high degree of competition and low barriers to entry in most of our markets. Accordingly, we devote considerable attention to operating unit management quality, stability, and contingency planning, including related considerations of compensation, and non-competition protection where applicable.
Economic and Industry Factors
As a mechanical and building controls services provider, we operate in the broader nonresidential construction services industry and are affected by trends in this sector. While we do not have operations in all major cities of the United States, we believe our national presence is sufficiently large that we experience trends in demand for and pricing of our services that are consistent with trends in the national nonresidential construction sector. As a result, we monitor the views of major construction sector forecasters along with macroeconomic factors they believe drive the sector, including trends in gross domestic product, interest rates, business investment, employment, demographics, and the fiscal condition of federal, state and local governments.
Spending decisions for building construction, renovation and system replacement are generally made on a project basis, usually with some degree of discretion as to when and if projects proceed. With larger amounts of capital, time, and discretion involved, spending decisions are affected to a significant degree by uncertainty, particularly concerns about economic and financial conditions and trends. We have experienced periods of time when economic weakness caused a significant slowdown in decisions to proceed with installation and replacement project work.
Operating Environment and Management Emphasis
Nonresidential building construction and renovation activity, as reported by the federal government, declined steeply over the four-year period from 2009 to 2012, and 2013 and 2014 activity levels were relatively stable at the low levels of the preceding years. During the four-year period from 2015 to 2018, there was an increase in overall activity levels and we currently expect that activity will continue at these improved levels during 2019.
As a result of our continued strong emphasis on cash flow, at March 31, 2019 we had modest indebtedness under our revolving credit facility, with positive uncommitted cash balances, as discussed further in “Liquidity and Capital Resources” below. We have a credit facility in place with terms we believe are favorable that does not expire until April 2023. We have strong surety relationships to support our bonding needs, and we believe our relationships with the surety markets are strong and benefit from our operating history and financial position. We have generated positive free cash flow in each of the last twenty calendar years and will continue our emphasis in this area. We believe that the relative size and strength of our balance sheet and surety relationships as compared to most companies in our industry represent competitive advantages for us.
As discussed at greater length in “Results of Operations” below, we expect price competition to continue as our customers and local and regional competitors respond cautiously to improved market conditions. We will continue to invest in our service business, to pursue the more active sectors in our markets, and to emphasize our regional and national account business. Our primary emphasis for 2019 is on execution and cost control, but we are seeking growth based on our belief that industry conditions will continue to be strong in the near term, and we believe that activity levels will permit us to continue to earn solid profits while preserving and developing our workforce. We continue to focus on project qualification, estimating, pricing and management; and we are investing in growth and improved performance.
Cyclicality and Seasonality
Historically, the construction industry has been highly cyclical. As a result, our volume of business, particularly in new construction projects and renovation, may be adversely affected by declines in new installation and replacement projects in various geographic regions of the United States during periods of economic weakness.