As a user with multiple monitors attached to my Mac, how does it select which one a new window is opened on? I have a Macintosh [MacBook Pro] with multiple monitors. There's the built in laptop display and I additional have a Apple Thunderbolt Display and another third party monitor attached via Thunderbolt/DisplayPort adapter. This is a total of three displays. 

When, in an application, I open a new window, the new window doesn't often open on the display I which currently had focus, but seems to open randomly across the three displays. That is I may have an open, active, foreground window on the Thunderbolt Display and when cmd-N'ing to open a new window it may open on the laptop screen or the third display. 

How is Mac OS X deciding which display to open the new window on and can this be selectively changed to alway open on the currently active display?
If you right click on any icon in your dock, you could assign an app to a display.