This book by former Detachment "A" member James Stejskal is a great history of a highly specialized unit. I always thought this unit was simply a forward deployed element of 10th Group; it was not.
The skill set and mission(s) of this unit were unlike anything else in the military at that time. They were a blend of OSS and SF and trained for scenarios that other SF units did not.
Interestingly, this unit was the father of modern Counter Terrorism operations and techniques. Beckwith and Marchinko actually went to them to get their SOPs.
It's not a super enthralling read but readable and well worth it to learn about this unique and highly trained unit.