Place pork in a shallow dish and season with salt and pepper.
Combine garlic, thyme, balsamic, mustards and olive oil in a small bowl. Season with salt and pepper. Pour half over pork. Rub glaze over pork and let sit at room temperature for 30 minutes.
Transfer pork to a roasting pan fitted with a rack and pour 1-1/2 cups (355 milliliters) water into bottom of pan. Roast until internal temperature reaches 140°F (60°C), about one hour, basting with reserved glaze every ten minutes after first 30 minutes of cooking. Add more water if pan becomes dry.
Transfer to a cutting board, cover with aluminum foil and rest for ten minutes before slicing to serve.