My husband and daughters relationship.

My husband (36) and daughter (15) spend slot of time together. She tells him everything yet she doesn't keep it from me when I ask her. For example when I come home from work (my husband gets home before and is there when she comes home from school) I see them laughing and they see me but stop. Later I'll ask her what they talked about and without hesitation she'll tell me. I just want to know if it is normal that they are so open about her sex life as well since I recently overheard them talking about it, or should I be concerned?