The luxury U.S. real estate market has been on fire in recent years, thanks to an influx of foreign capital. Philip White, president and CEO of Sotheby's International Realty, is bullish on 2017. "We're still seeing good activity from China and to some degree South America," he said, referring to New York City real estate priced north of $50 million. "New York City remains a save haven for investors and I think that will remain that way," he said.