Stored Procedure, Insert with subquery

I want to create a stored procedure that uses a subquery to insert the max Identity from a table into another table (last record added)  
I wrote the code but it says that sub queries are not allowed in the insert statements, only scalar expressions.  If its not possible, how do I use the same select statement to save the return to a scalar value?

CREATE PROCEDURE NewCaseInsertDocs 
	-- Add the parameters for the stored procedure here
	@MaxCaseId int
 
AS
BEGIN
	-- SET NOCOUNT ON added to prevent extra result sets from
	-- interfering with SELECT statements.
	SET NOCOUNT ON;
	
    -- Insert statements for procedure here
  	INSERT INTO dbo.Documents_Needed 
	                      (CaseID, Type)
	VALUES     ((SELECT MAX(CaseID) From dbo.ACF_Cases),'Assign')
END
GO

Select allOpen in new window