I am helping my parents with their taxes, They have moved to an assisted living community and moved all of their mutual fund investments out of the stock market and into

of the stock market and into their money market.  They had a large capital gain as a result.  TurboTax is printing estimated tax payment coupons for 2017 due to the disparity in their income from 2015 to 2016.  The capital gain is a one-time event. Do they really have to pay estimated taxes in 2017?  Their income will return to the 2015 level in 2017.