"It's a no-brainer"... but when should the Board get involved?

I'd like to share a small quandary with you. The last month has involved a lot of activity around some of my Boards - the main reason for the relative silence on this page.

A couple of weeks ago, on a Saturday morning, our company's legal adviser rang to ask if I would sign an urgent document that needed the signature of two directors. I don't need to go into the details, but it related to a fairly large transaction, which I knew was coming up. But it had emerged since our previous Board meeting and we'd never discussed it together as a Board.  

I talked it over with our lawyer and asked whether he thought this was a matter that ought to go to the Board first. 'Well, it's really a no-brainer, isn't it?' was his reply. I agreed, and signed. I did ask him to confirm that in his opinion it was in the best interests of the company for us to sign this document, which he did. 

Looking back though, should I have pushed back a little harder? Certainly, there was some urgency about the transaction. And yes, I did (and still do) believe that going ahead was in the company's best interest (one of the legal tests for a director's actions). But I have this feeling that we might have been a little lax in our process. All Board members had seen the emails on the subject, so I suppose they could have raised any concerns. But my main question is where the boundary is: when does a 'no-brainer' become a 'half-brainer', or a matter that might actually benefit from some considered Board discussion, or finally a decision that really needed some thorough testing? And who decides where these borders are? After all, part of our reason for being there is to test and challenge management thinking.  

As directors, we don't usually do much in our individual capacity, and the whole Board is likely to be responsible for the actions of any of us. So the other directors were - possibly without knowing it - putting their faith in the two of us who agreed to sign.

I think I have learned from the experience. If I'm in the same position again - whatever the need for haste - I think I'll at least ask for a Board conference call to discuss it first - as much for the benefit of the other directors as for my own peace of mind. 

We've just had another Board meeting, at which the Board ratified our actions. What if they hadn't? I'd be interested in any similar experiences you may have had - and what you did.