A B737 Captain reported inadvertently bumping the number one engine start lever out of the idle position with the the Logbook. The engine began to spool down and the lever is quickly returned to the idle position. Flight continued to destination.

Narrative

Cruising at FL380; I needed to make a logbook entry detailing some auto throttle and FMS problems we had encountered on departure. While maneuvering the logbook from the side pocket of the center pedestal on the Captain's side below the trim wheel I apparently bumped the number one engine start lever with the edge of the logbook; causing it to come out of the 'idle' DETENT and move approximately one inch towards 'cutoff'. My First Officer called out an RPM decrease and applied manual ignition. Putting the logbook aside; I immediately noticed the position of the start lever and placed it back in the 'idle' DETENT; then retarded the throttle to idle. The minimum engine RPM observed was approximately 45% N1. It recovered immediately with normal engine indications at both idle and cruise power. No exceedence observed. An initial descent was requested and initiated; but the IAS decrease was only about ten knots. All power was restored within fifteen to twenty seconds. Descent was stopped at FL360. Since the cause of the rollback was known; not mechanically caused; and all systems were normal; we continued flight to destination. Made contact with cabin crew and subsequently made PA confirming all systems were normal.