Final answer:
The sentence that states the main idea is: All in all, it was the best years in the history of the company.
Step-by-step explanation:
The sentence that states the main idea is: All in all, it was the best years in the history of the company. This sentence summarizes the previous sentences that mention low costs, high output, a good person for each job, and a firm market. It highlights that the mentioned factors made it the best years in the history of the company.