In March, security expert Brian Krebs of KrebsonSecurity noted:
The Facebook source said the investigation so far indicates between 200 million and 600 million Facebook users may have had their account passwords stored in plain text and searchable by more than 20,000 Facebook employees. The source said Facebook is still trying to determine how many passwords were exposed and for how long, but so far the inquiry has uncovered archives with plain text user passwords dating back to 2012.
My Facebook insider said access logs showed some 2,000 engineers or developers made approximately nine million internal queries for data elements that contained plain text user passwords. -KrebsonSecurity
In short, if you believe Facebook that the passwords were not improperly accessed, rest well. If you don't believe them, and you use your Instagram password for other things, perhaps it's time to think of a new one.