In particular, the La Jolla and nearby Sorrento Valley areas are home to offices and research facilities for numerous biotechnology companies. Major biotechnology companies like Illumina and Neurocrine Biosciences are headquartered in San Diego, while many other biotech and pharmaceutical companies have offices or research facilities in San Diego. San Diego is also home to more than 140 contract research organizations (CROs) that provide contract services for pharmaceutical and biotechnology companies. According to the City's 2016 Comprehensive Annual Financial Report, the top employers in the city are:  San Diego has high real estate prices. San Diego home prices peaked in 2005, and then declined along with the national trend. As of December 2010, prices were down 36 percent from the peak, median price of homes having declined by more than $200,000 between 2005 and 2010. As of May 2015, the median price of a house was $520,000. In November 2018 the median home price was $558,000. The San Diego metropolitan area had one of the worst housing affordability rankings of all metropolitan areas in the United States in 2009. Consequently, San Diego has experienced negative net migration since 2004. A significant number of people moved to adjacent Riverside County, commuting daily to jobs in San Diego, while others are leaving the region altogether and moving to more affordable regions. The city is governed by a mayor and a nine-member city council. In 2006, its government changed from a council–manager government to a strong mayor government, as decided by a citywide vote in 2004. The mayor is in effect the chief executive officer of the city, while the council is the legislative body. The City of San Diego is responsible for police, public safety, streets, water and sewer service, planning and zoning, and similar services within its borders. San Diego is a sanctuary city, however, San Diego County is a participant of the Secure Communities program. , the city had one employee for every 137 residents, with a payroll greater than $733 million. The members of the city council are each elected from single-member districts within the city. The mayor and city attorney are elected directly by the voters of the entire city. The mayor, city attorney, and council members are elected to four-year terms, with a two-term limit. Elections are held on a non-partisan basis per California state law; nevertheless, most officeholders do identify themselves as either Democrats or Republicans. In 2007, registered Democrats outnumbered Republicans by about 7 to 6 in the city, and Democrats currently () hold a 6–3 majority in the city council.