Net investment income increased 4% over the prior year. In addition, excess investment income, a measure used by management as explained below, increased by 2% over the prior year.
The following represents net income and net operating income from continuing operations for the 3 years ended December 31, 2018.
The Liberty National Exclusive Agency markets individual and group life insurance to lower middle to middle-income customers. Life premium income for this agency was $279 million in 2018, an increase of 2% from $275 million in 2017. Life premium income in 2016 totaled $270 million. Net sales increased 5% during 2018 to $49 million over the 2017 total of $47 million. Net sales in 2017 increased 17%. The continued increases in net sales reflect changes in structure of the agency that were put in place several years ago. Recent growth in middle management within the agency should help continue this growth. First-year collected premium increased 10% to $36 million during 2018 and increased 14% in 2017 to $33 million.
We plan to use excess cash available at the Parent Company as efficiently as possible in the future. Possible uses of excess cash flow include, but are not limited to, share repurchases, acquisitions, increases in shareholder dividends, investment in securities, or repayment of short-term debt. We will determine the best use of excess cash after ensuring that targeted capital levels are maintained in our companies. If market conditions are favorable, we currently expect that share repurchases will continue to be a primary use of those funds.
Advertising Costs: Costs related to advertising are generally charged to expense as incurred. However, certain Globe Life Direct Response advertising costs are capitalized when there is a reliable and demonstrated relationship between total costs and future benefits that is a direct result of incurring these costs. Globe Life Direct Response advertising costs consist primarily of the production and distribution costs of direct mail advertising materials, and when capitalized are included as a component of DAC. They are amortized in the same manner as other DAC. Globe Life Direct Response advertising costs charged to earnings and included in other operating expense were $9.0 million, $9.3 million, and $9.3 million in 2018, 2017, and 2016, respectively. At December 31, 2018, unamortized capitalized advertising costs included within DAC were $1.3 billion at December 31, 2018 and $1.3 billion at December 31, 2017.
Securities, cash, and short-term investments held on deposit with various state and federal regulatory authorities had an amortized cost and fair value, respectively, of $712 million and $763 million at December 31, 2018 and $657 million and $753 million at December 31, 2017.
Corporate debt securities and redeemable preferred stocks represent 83% of Torchmark's investment portfolio. These investments are spread across a wide range of industries. Below are the ten largest industry concentrations held in the corporate portfolio of corporate debt securities and redeemable preferred stocks at December 31, 2018, based on fair value:
Commercial mortgage loan participations: Summaries of commercial mortgage loan participations at December 31, 2018 and 2017 are as follows:
Plan assets in the funded plans consist primarily of investments in marketable fixed maturities and equity securities that are valued at fair value. Torchmark measures the fair value of its financial assets, including the assets in its benefit plans, in accordance with accounting guidance which establishes a hierarchy for asset values and provides a methodology for the measurement of value. Please refer to Note 1-Significant Accounting Policies under the caption Fair Value Measurements, Investments in Securities for a complete discussion of valuation procedures. The following table presents the assets of Torchmark’s defined benefit pension plans for the years ended December 31, 2018 and 2017.