General and administrative expenses increased by $38,806,000, or 90.3%, to $81,762,000 for the year ended December 31, 2017, from $42,956,000 for the year ended December 31, 2016, primarily due to amortization costs related to the merger with AmCo.
We classify all of our investments as available-for-sale. Our investments at December 31, 2018 and 2017 consisted mainly of U.S. government and agency securities, states, municipalities and political subdivisions and securities of investment-grade
corporate issuers. Our equity holdings consisted mainly of securities issued by companies in the energy, consumer products, financial, technology and industrial sectors. Most of the corporate bonds we hold reflected a similar diversification. At December 31, 2018, approximately 87.2% of our fixed maturities were U.S. Treasuries, or corporate bonds rated “A” or better, and 12.8% were corporate bonds rated “BBB” or “BB”.
The following table summarizes our expected payments for contractual obligations at December 31, 2018:
We report both basic earnings per share and diluted earnings per share. To calculate basic earnings per share, we divide net income attributable to UIHC common stockholders (net income less the net income attributable to NCI) by the weighted-average number of shares of common stock outstanding during the period. We calculate diluted earnings per share using the Treasury method by dividing net income attributable to UIHC common stockholders by the weighted-average number of shares of common stock, common stock equivalents, and restricted shares outstanding during the period. Common share equivalents are only included when they are dilutive.
We write flood insurance under an agreement with the National Flood Insurance Program. We cede 100% of the premiums written and the related risk of loss to the federal government. We earn commissions for the issuance of flood policies based upon a fixed percentage of net written premiums and the processing of flood claims based upon a fixed percentage of incurred losses, and we can earn additional commissions by meeting certain growth targets for the number of in-force policies. We recognized commission revenue from our flood program of $1,575,000, $1,255,000, and $1,056,000 for the years ended December 31, 2018, 2017, and 2016, respectively.
Each of these methods has its own strengths and weaknesses that depend upon the circumstances of the segment and the age of the claims experience we analyze. The nature of our book of business allows us to place substantial, but not exclusive, reliance on the loss development methods, and the selected LDFs, represent the most critical aspect of our loss reserving process. We use the same set of LDFs in the methods during our loss reserving process that we also use to calculate the premium necessary to pay expected ultimate losses.
In addition, the BB&T note requires that we establish and maintain with BB&T at all times during the term of the loan a noninterest bearing demand deposit account with a minimum balance of $500,000, and an interest-bearing account with a minimum balance of $1,500,000. In the event of default, BB&T may, among other things, declare its loan immediately due and payable, require us to pledge additional collateral to the bank, and take possession of and foreclose upon our corporate headquarters, which has been pledged to the bank as security for the loan. At December 31, 2018, we were in compliance with the covenants as specified in the BB&T note.