Thanks, Peter. I appreciate your response.
Ultimately we've done very little to raise our site DA's in the past outside of writing content centered around popular keywords. Only in the last three weeks I launched a guest posting campaign, targeting relevant sites with a higher DA than our own. From my understanding, this is a relatively safe way to force the issue provided you're providing sites with good content.
Over the past two months I've seen many of our sites decline in DA by about 4-5 points. Not sure if we've been doing anything to directly cause this, I've heard it could just be a change to the Moz algorithm. I've noticed competing sites have also declined in recent weeks.