Getting the first instance of a key/value out of response body

Since my response is just a string, how can i use a check to save the first instance of documentId within my session?

{
“status”: “Success”,
“results”: [
{
“name”: “some name”,
“documentId”: “someId”,
},
{
“name”: “another name”,
“documentId”: “anotherId”,
}
]
}

https://github.com/excilys/gatling/wiki/Checks#wiki-regex

https://github.com/excilys/gatling/wiki/Checks#wiki-json