Copying and pasting keys for run-cycle

I have a run-cycle which is 18 frames in length. I'd like to extend the scene to
72 frames with the existing cycle repeating three more times. How do I copy
keyframes for the whole animation?   I did copy the key frames for controllers
on by one, then pole vectors, IK chains for arms and legs, and my character was
sadly all over the place as I replayed the animation. Pleas