Answer based on context:

After winning at home against the Ravens, the Steelers traveled to Oakland to take on the Raiders.  The Raiders got off to a fast start in the 1st quarter when Terrelle Pryor ran for a 93-yard touchdown to take a 7-0 lead.  This remains the longest touchdown run by any QB in NFL history.  Darren McFadden ran into the end zone for a 7-yard touchdown run to make the score 14-0.  The Steelers managed to get on the board in the 2nd quarter when Shaun Suisham nailed a 47-yard field goal for a 14-3 deficit.  But the Raiders moved ahead as McFadden ran for another touchdown from 4 yards out for a 21-3 score at halftime.  After a scoreless 3rd quarter, the Steelers went back to work in the 4th quarter as Ben Roethlisberger found Emmanuel Sanders on a 9-yard touchdown pass to make the score 21-10 and then Le'Veon Bell ran for a 4-yard touchdown with the successful 2-point conversion to make the final score 21-18 as their comeback attempt again was cut short and the team fell to 2-5.  On a positive note, they had won 2 out of their last 3 games coming off their bye week.

How many points did the Steelers lose by?
3