Do I need to include page numbers when citing indirectly in the text?
It depends on the context, of course. 

I am a reviewer on an academic journal and there, we ask authors for the page. 

I've also been told by a prof that, for a homework essay, he only spot checks a few cites because he "knows the author's voice," (may be more applicable to certain fields than to others) and if the quote is suspect then he will check more thoroughly. If I were you, I'd include the page cite just to be safe. I'm assuming this is for a class - has your prof said anything about how stringent the cites need to be? That would be more determinative than SE's speculation.