Non-GAAP operating (loss) earnings, non-GAAP operating (loss) earnings per common share, non-GAAP operating return on average common equity and underwriting loss are non-GAAP financial measures. Please see "Key Financial Measures" for additional information and a reconciliation to the nearest U.S. GAAP financial measure of net (loss) income.
Please refer to "Notes to Consolidated Financial Statements - Note 13. Earnings per Common Share" included under Item 8 "Financial Statements and Supplementary Data" of this Annual Report on Form 10-K for the calculation of basic and diluted (loss) earnings per common share.
We historically have derived the majority of our revenues from premiums on reinsurance contracts, net of any reinsurance or retrocessional coverage purchased and to a minor extent from premiums from insurance policies. Reinsurance premiums are a function of the amount and types of policies and contracts we write, as well as prevailing market prices. Our prices are determined before our ultimate costs, which may extend far into the future, are known.
Please refer to "Notes to Consolidated Financial Statements - Note 5. Fair Value of Financial Instruments" included under Item 8 "Financial Statements and Supplementary Data" of this Annual Report on Form 10-K on page for a discussion on the fair value methodology and valuation techniques used by the Company to determine the fair value of the financial instruments held at December 31, 2018 and 2017.
dividends paid to preference shareholders decreased to $29.2 million compared to preferred dividends of $33.8 million for the same period in 2016 due to the conversion of the 7.25% Mandatory Convertible Preference Shares - Series B into our common shares on September 15, 2016. This was partly offset by dividends paid on the 6.7% Preference Shares - Series D that were issued on June 15, 2017.
On June 15, 2016, Maiden NA fully redeemed its 2011 Senior Notes using the proceeds from the 2016 Senior Notes issuance. The 2011 Senior Notes were redeemed at a redemption price equal to 100% of the principal amount of $107.5 million plus accrued and unpaid interest on the principal amount being redeemed up to, but not including, the redemption date. As a result, we accelerated the amortization of the remaining 2011 Senior Notes issuance cost of $2.3 million during the year ended December 31, 2016.
The table below shows net premiums written by line of business for the years ended December 31, 2018 and 2017:
Commission and Other Acquisition Expenses - Commission and other acquisition expenses increased by $1.2 million, or 0.2%, for the year ended December 31, 2018 compared the same period in 2017. The commission and other acquisition expense ratio remained flat at 32.2% for the years ended December 31, 2018 and 2017. The fluctuations in the ratios during the year ended December 31, 2018 compared to 2017 reflect the change in the mix of business and is also affected by lower commission associated with the retrocession premium ceded during the year ended December 31, 2018 compared to the same period in 2017.
Net premiums earned increased by $66.0 million, or 3.6% for the year ended December 31, 2017 compared to the same period in 2016. The increase is primarily due to AmTrust's prior year premium written growth as well as lower utilization of retrocessional capacity in the current period. The table below details net premiums earned by line of business for the years ended December 31, 2017 and 2016:
Maiden Holdings’ wholly owned U.K. subsidiary, Maiden Global, operates as a reinsurance services and holding company, is subject to regulation by the U.K. Financial Conduct Authority (the "FCA") that limit the maximum amount of annual dividends or distributions paid by Maiden Global to the Company. At December 31, 2018, Maiden Global is allowed to pay dividends or distributions not exceeding $2.9 million. During 2018 and 2017, Maiden Global paid dividends to Maiden Holdings of $1.0 million and $0.7 million, respectively.
At December 31, 2018, 91.8% of the Company’s U.S. agency bond holdings are mortgage-backed. Additional details on the Agency MBS at December 31, 2018 and 2017 were as follows:
The following table summarizes the Company's other material balance sheet changes at December 31, 2018 and 2017:
Other assets decreased by 70.0% and other liabilities decreased by 27.3% as at December 31, 2018 compared to December 31, 2017. The decline in other assets and other liabilities is largely due to the commutation of our retrocessional quota share agreements
We have funded a portion of our capital requirements through issuances of senior securities, including secured and unsecured debt securities, or issuances of common or preference shares. For flexibility, we have a current universal shelf registration statement that allows for the public offering and sale of our debt securities, common shares, preference shares and warrants to purchase such securities. Our ability to fund a portion of our capital requirements through the issuance of debt or equity securities will depend on future market conditions, funding needs, our financial condition and other factors and there can be no assurance that any such issuance will occur or be successful or at terms Maiden or our regulator considers acceptable.
In the normal course of business, the Company is a party to a variety of contractual obligations as summarized below. These contractual obligations are considered by the Company when assessing its liquidity requirements and the Company is confident in its ability to meet all of its obligations. The Company’s aggregate contractual obligations at December 31, 2018 are as follows: