WordNet (r) 3.0 (2006):

thrash out
    v 1: discuss vehemently in order to reach a solution or an
         agreement; "The leaders of the various Middle Eastern
         countries are trying to hammer out a peace agreement" [syn:
         thrash out, hammer out]

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "thrash out":
   agitate, appraise, argue, argufy, assess, bandy words, bicker,
   canvass, catalog, categorize, cavil, choplogic, class, classify,
   contend, contest, cross swords, cut and thrust, debate, discept,
   dispute, evaluate, factor, gauge, give and take, group, hassle,
   have it out, identify, join issue, lock horns, logomachize, moot,
   pettifog, plead, polemicize, polemize, quibble, sift, sort,
   sort out, spar, take sides, try conclusions, weigh, winnow,
   wrangle