How to select default item in detail view for iPad? (in Split View Controller)

I solved this problem. I am writing to help others in the future.

func viewDidLoad() {
        //..
        let initialIndexPath = NSIndexPath(forRow: 0, inSection: 0)
        self.tableView.selectRowAtIndexPath(initialIndexPath, animated: true, scrollPosition:UITableViewScrollPosition.None)

        if UIDevice.currentDevice().userInterfaceIdiom == .Pad {
            self.performSegueWithIdentifier("ShowDetail", sender: initialIndexPath)
        }
}

func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if segue.identifier == "ShowDetail" {
            if sender!.isKindOfClass(UITableViewCell) {
                if let indexPath = self.tableView.indexPathForCell(sender as! UITableViewCell) {

                    // Get row from selected row in tableview

                }
            } else if sender!.isKindOfClass(NSIndexPath) {
                let tableCell = self.tableView.cellForRowAtIndexPath(sender as! NSIndexPath)
                let indexPath = self.tableView.indexPathForCell(tableCell!)

                // Get row from sender, which is an NSIndexPath
            }
        }
}