You'll want one of these, and then a DP Male to miniDP female adapter (as I don't think anyone currently makes a direct USB-C to miniDP adapter): http://www.monoprice.com/product?c_id=103&cp_id=10330&cs_id=1033001&p_id=13234&seq=1&format=2
(Or to make this easier, replace your monitor's miniDP cable with a regular cable, and you can skip the mini adapter)