We provide mortgage insurance (referred to as "mortgage insurance" or "MI") through our wholly owned insurance subsidiaries, National Mortgage Insurance Corporation (NMIC) and National Mortgage Reinsurance Inc One (Re One). NMIC and Re One are domiciled in Wisconsin and principally regulated by the Wisconsin Office of the Commissioner of Insurance (Wisconsin OCI). NMIC is our primary insurance subsidiary, and is approved as an MI provider by the GSEs and is licensed to write MI coverage in all 50 states and D.C. Re One provides reinsurance to NMIC on insured loans with coverage levels in excess of 25%, after giving effect to third-party reinsurance. Our subsidiary, NMI Services, Inc. (NMIS), provides outsourced loan review services to mortgage loan originators.
MI protects lenders and investors from default-related losses on a portion of the unpaid principal balance of a covered mortgage. MI plays a critical role in the U.S. housing market by mitigating mortgage credit risk and facilitating the secondary market sale of high loan-to-value (LTV) (i.e. above 80%) residential loans to the GSEs, who are otherwise restricted by their charters from purchasing or guaranteeing high-LTV mortgages that are not covered by certain credit protections. Such credit protection and secondary market sales allow lenders to increase their capacity for mortgage commitments and expand financing access to existing and prospective homeowners.
NMI Holdings, Inc. (NMIH), a Delaware corporation, was incorporated in May 2011, and we began start-up operations in 2012 and wrote our first MI policy in 2013. Since formation, we have sought to establish customer relationships with a broad group of mortgage lenders and build a diversified, high-quality insured portfolio. As of December 31, 2018, we had master policies with 1,374 customers, including national and regional mortgage banks, money center banks, credit unions, community banks, builder-owned mortgage lenders, internet-sourced lenders and other non-bank lenders. As of December 31, 2018, we had $71.5 billion of total insurance-in-force (IIF), including primary IIF of $68.6 billion, and $17.2 billion of gross risk-in-force (RIF), including primary RIF of $17.1 billion. For the year ended December 31, 2018, we generated new insurance written (NIW) of $27.3 billion. As of December 31, 2018, we had 304 full-time employees.