Its likely been built in house theres no obvious markers that it was built by a dev company - unless the contract was such that they couldn't have a link/mention on the site (because a lot of developers like to have there name on a site where they can because its much better publicity than just mentioning on there own site)
I cant see any obvious tell tail signs of a particular CMS being used from viewing the html source
server headers show apache so its very probably a custom built PHP application rather than a specific CMS - especially as there site functions are not easily performed by most existing CMS/Applications out of the box (not saying its impossible but likely much simpler to do with a custom build)
