Personal lines - Total personal lines premiums written increased 4.9% to $5.3 billion in 2019, from $5.0 billion in 2018, driven by an increase of 1.8% in total personal lines policies in force and an increase of 2.9% in the total personal lines year-over-year average premium per policy.
Commissions - Commissions increased $40.9 million in 2019 compared to 2018 and $36.3 million in 2018 compared to 2017. The increases in both periods resulted from higher direct and affiliated assumed premiums written by the Exchange, somewhat offset by lower agent incentive costs related to less profitable growth.
Serving in the capacity of attorney-in-fact for the Exchange, we are dependent on the growth and financial condition of the Exchange, who is our sole customer. The strength of the Exchange and its wholly owned subsidiaries is rated annually by A.M. Best Company. Higher ratings of insurance companies generally indicate financial stability and a strong ability to pay claims. The ratings are generally based upon factors relevant to policyholders and are not directed toward return to investors. The Exchange and each of its property and casualty subsidiaries are rated A+ "Superior". On June 24, 2019, the outlook for the financial strength rating was affirmed as stable. According to A.M. Best, this second highest financial strength rating category is assigned to those companies that, in A.M. Best's opinion, have achieved superior overall performance when compared to the standards established by A.M. Best and have a superior ability to meet obligations to policyholders over the long term. Only approximately 12% of insurance groups are rated A+ or higher, and the Exchange is included in that group.
Other investments primarily include agent loans. Agent loans are included with other assets in the Statements of Financial Position.
The following table presents a breakdown of the fair value of our fixed maturity portfolio by sector and rating as of December 31, 2019: (1)
In 2019, 2018 and 2017, we purchased shares of our outstanding Class A nonvoting common stock outside of our publicly announced share repurchase program for certain stock-based incentive plans. We purchased 15,003 shares for $2.6 million in 2019 and 27,120 shares for $3.2 million in 2018 for our equity compensation plan and to fund the rabbi trust for the outside director deferred stock compensation plan and the incentive compensation deferral plan. In 2017, we purchased 60,332 shares for $7.3 million for our long-term incentive plan, to fund the rabbi trust for the outside director deferred stock compensation plan, and for our equity compensation plan. All shares were delivered in the year they were purchased.
If a decline is deemed to be other-than-temporary, an assessment is made to determine the amount of the total impairment related to a credit loss and that related to all other factors. Consideration is given to all available information relevant to the collectability of the security in this determination. When the entire amortized cost basis of the security will not be recovered, a credit loss exists. For securities with credit impairments that we did not intend to sell, the credit portion of the loss would be recorded through net income and the non-credit portion of the impairment would be recorded in other comprehensive income. Currently, we have the intent to sell all of our securities that have been determined to have a credit-related impairment. As a result, the entire amount of any impairment is recognized in earnings.
Limited partnership investments - Limited partnership investments primarily include U.S. and foreign private equity investments and are recorded using the equity method of accounting. The partnerships record assets on their balance sheet at fair value. While we perform various procedures in review of the general partners' valuations, we rely on the general partners' financial statements as the best available information to record our share of the partnership unrealized gains and losses resulting from valuation changes. Due to the availability of financial statements provided by the general partner, our share of limited partnership results is generally recorded on a quarter lag within equity in earnings (losses) of limited partnerships. Cash contributions made to and distributions received from the partnerships are recorded in the period in which the transaction
The majority of our revenue is derived from the subscriber’s agreement between us and the subscribers (policyholders) at the Exchange. Pursuant to the subscriber’s agreement, we earn a management fee calculated as a percentage, not to exceed 25%, of all direct and affiliated assumed written premiums of the Exchange. We account for management fee revenue in accordance with ASC 606, which we adopted in 2018. See Note 2, "Significant Accounting Policies".
The limited partnership investment measured at fair value represents one real estate fund included on the balance sheet as a limited partnership investment reported under the fair value option using the net asset value (NAV) practical expedient, which is not required to be categorized in the fair value hierarchy. The fair value of this investment is based on our proportionate share of the NAV from the most recent partners' capital statements received from the general partner, which is generally one quarter prior to our balance sheet date. We consider observable market data and perform a review validating the appropriateness of the NAV at each balance sheet date. Liquidation of this fund was completed in January 2019.
As of December 31, 2019, we have access to a $100 million bank revolving line of credit with a $25 million letter of credit sublimit that expires on October 30, 2023. As of December 31, 2019, a total of $99.1 million remains available under the facility due to $0.9 million outstanding letters of credit, which reduces the availability for letters of credit to $24.1 million. We had no borrowings outstanding on our line of credit as of December 31, 2019. Investments with a fair value of $110.1 million were pledged as collateral on the line at December 31, 2019. The securities pledged as collateral have no trading restrictions and are reported as available-for-sale securities and cash and cash equivalents as of December 31, 2019. The banks require compliance with certain covenants, which include leverage ratios and debt restrictions, for our line of credit. We are in compliance with all covenants at December 31, 2019.
Projected benefit obligations increased $168.3 million at December 31, 2019 compared to December 31, 2018 due primarily to actuarial losses resulting from the lower discount rate discount rate used to measure the future benefit obligations. The discount rate decreased to 3.59% in 2019 from 4.47% in 2018. The increase in benefits paid of $25.4 million in 2019 compared to 2018 was primarily due to a pension plan amendment offering a one-time lump sum payment to former vested employees.
(1) Forfeitures are the result of plan participants who separated from service with the Company.