Finding an element by partial id with Selenium in C#

I am trying to locate an element with a dynamically generated id. The last part of the string is constant ("ReportViewer_fixedTable"), so I can use that to locate the element. I have tried to use regex in XPath:

targetElement = driver.FindElement(
    By.XPath("//table[regx:match(@id, "ReportViewer_fixedTable")]"));

And locating by CssSelector:

targetElement = driver.FindElement(
    By.CssSelector("table[id$='ReportViewer_fixedTable']"));

Neither works. Any suggestions would be appreciated.