With no documents opened, go to Preferences > Interface, and check 'Open Documents as Tabs'.
This is for CS6 on Windows.
On Mac and/or other versions may slightly vary.
Ick, is that the only way? I hate them opening as tabs and have always kept that turned off
Maybe like having them open at 80% the size of what the Indesign field is?
There's no such control...
You're out of luck then, I'm afraid.
In the early days you could 'maximize' doc window, now they are arranged in tabs.
Not so bad decision, imo.
You still can 'maximize', but it works, hm... a bit different...
Btw, you'll find the same picture in Photoshop, too.