Is your dad still a detective with 〜のだ

Grammar Explanation

名探偵コナン » Volume 1 » Page 12

Ran seems angry as Shin’ichi basks in the media attention he’s getting for solving a difficult case. When Shin’ichi asks Ran why she’s angry, she points out that it’s because of Shin’ichi that her father’s been getting fewer case requests.

“I’m not at all angry!”
“Huh? Your dad was still working as a detective?”
Literal: “Huh? Is it that your dad was still working as a detective?”

Shin’ichi has the incomplete observation that Ran’s father is losing work taking cases because of Shin’ichi’s detective work.

Considering how bad Ran’s father is at being a detective, it’s surprising to Shin’ichi that he’s still in the detective business.

However, based on Ran’s remark, Shin’ichi reasons that her father must still be working as a detective. He puts this as a question for confirmation.