What is the author's style in The Assassination of Jesse James by the Coward Robert Ford by Ron Hansen?

The book reads almost like a history book with detailed accounts of many of the robberies and other exploits of Jesse James, his brother Frank and other members of the gang. The author seems to become bogged down at time in revealing the details, such as the name of the man who slipped out into the alley during a particular hold up but who was armed only with birdshot. Other details include specific amounts of money they steal from various robberies and the names of men who were hurt or killed by Jesse and his gang.