The hang analyzer will log things like:

[2018/12/20 16:22:29.931] MongoDB Lock at 0x10024bc0c00 held by Idle Transaction (LockerId 358) (mongo::MODE_IX) waited on by "conn36" (Thread 0x3fff849deda0 (LWP 34093))

This doesn't give much information about the idle transaction. Logging the SessionID and txnNumber of the transaction, and maybe even what namespaces the statements were on would be very helpful.