phrasal verb
Definition 1
Arrive at, obtain (agreement, harmony) by a process of discussion and debate.
Source: Invertext, based on Concise Oxford Dictionary
Context: But now that the details [of the European Commission project to improve risk and capital management of insurers] are being thrashed out [...] the howls of protest from some parts of the sector are getting louder.
Source: Financial Times 02/09/2009