Humana Pharmacy Solutions® script volumes for the Retail and Employer Group segment membership increased to approximately 274 million in 2013, up 15% versus scripts of approximately 238 million in 2012.
Services revenue increased $257 million or 25.1% from 2012 to $1.3 billion for 2013 primarily due to the acquisitions of Metropolitan and SeniorBridge as well as growth in our provider services operations.
Our 5-year $1.0 billion unsecured revolving credit agreement expires July 2018. Under the credit agreement, at our option, we can borrow on either a competitive advance basis or a revolving credit basis. The revolving credit portion bears interest at either LIBOR plus a spread or the base rate plus a spread. The LIBOR spread, currently 110 basis points, varies depending on our credit ratings ranging from 90 to 150 basis points. We also pay an annual facility fee regardless of utilization. This facility fee, currently 15 basis points, may fluctuate between 10 and 25 basis points, depending upon our credit ratings. The competitive advance portion of any borrowings will bear interest at market rates prevailing at the time of borrowing on either a fixed rate or a floating rate based on LIBOR, at our option.
As of December 31, 2014, we were not involved in any special purpose entity, or SPE, transactions. For a detailed discussion off-balance sheet arrangements, please refer to Note 16 to the consolidated financial statements included in Item 8. - Financial Statements and Supplementary Data.
Approximately 96% of our debt securities were investment-grade quality, with a weighted average credit rating of AA- by S&P at December 31, 2014. Most of the debt securities that were below investment-grade were rated BB, the higher end of the below investment-grade rating scale. Our investment policy limits investments in a single issuer and requires diversification among various asset types.
Humana Inc., headquartered in Louisville, Kentucky, is a leading health and well-being company focused on making it easy for people to achieve their best health with clinical excellence through coordinated care. The company’s strategy integrates care delivery, the member experience, and clinical and consumer insights to encourage engagement, behavior change, proactive clinical outreach and wellness for the millions of people we serve across the country. References throughout these notes to consolidated financial statements to “we,” “us,” “our,” “Company,” and “Humana,” mean Humana Inc. and its subsidiaries. We derived approximately 73% of our total premiums and services revenue from contracts with the federal government in 2014, including 15% related to our federal government contracts with the Centers for Medicare and Medicaid Services, or CMS, to provide health insurance coverage for individual Medicare Advantage members in Florida. CMS is the federal government’s agency responsible for administering the Medicare program.
Investment securities, which consist entirely of debt securities, have been categorized as available for sale and, as a result, are stated at fair value. Investment securities available for current operations are classified as current assets.
The following table presents details of our other intangible assets included in other long-term assets in the accompanying consolidated balance sheets at December 31, 2014 and 2013:
The terms of the credit agreement include standard provisions related to conditions of borrowing, including a customary material adverse effect clause which could limit our ability to borrow additional funds. In addition, the credit agreement contains customary restrictive and financial covenants as well as customary events of default, including financial covenants regarding the maintenance of a minimum level of net worth of $7.8 billion at December 31, 2014 and a maximum leverage ratio of 3.0:1. We are in compliance with the financial covenants, with actual net worth of $9.6 billion and actual leverage ratio of 1.4:1, as measured in accordance with the credit agreement as of December 31, 2014. In addition, the credit agreement includes an uncommitted $250 million incremental loan facility.
The fair value of shares vested was $99 million during 2014, $52 million during 2013, and $75 million during 2012. Total compensation expense not yet recognized related to nonvested restricted stock was $92 million at December 31, 2014. We expect to recognize this compensation expense over a weighted-average period of approximately 1.7 years. There are no other contractual terms covering restricted stock once vested.
We lease facilities, computer hardware, and other furniture and equipment under long-term operating leases that are noncancelable and expire on various dates through 2027. We sublease facilities or partial facilities to third party tenants for space not used in our operations. Rent with scheduled escalation terms are accounted for on a straight-line basis over the lease term. Rent expense and sublease rental income, which are recorded net as an operating cost, for all operating leases were as follows for the years ended December 31, 2014, 2013 and 2012:
At December 31, 2014, our military services business, which accounted for approximately 1% of our total premiums and services revenue for the year ended December 31, 2014, primarily consisted of the TRICARE South Region contract. The current five-year South Region contract, which expires March 31, 2017, is subject to annual renewals on April 1 of each year during its term at the government’s option. On January 27, 2015, we received notice from the Defense Health Agency, or DHA, of its intent to exercise its option to extend the TRICARE South Region contract through March 31, 2016.