using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		var line = "ID is PK_myid some more words\nID is PK_ my id some more words";
    	var pattern = @"\bID\s+is\s+(\w+(?:\s+\w+)*?)\s+some\b";
    	var output = Regex.Matches(line, pattern)
		    .Cast<Match>()
		    .Select(x => x.Groups[1].Value);
        foreach (var s in output)
        	Console.WriteLine(s);
	}
}