UISplitViewController - showDetailViewController(_ vc: UIViewController, sender: Any?) stacking view controllers.

Using UISplitViewController for displaying contact list and contact details screen. Primary, I have UITableViewController. On didSelectRow: set segue/programatically handle delegate to call showDetailViewControler. it always pushes viewController. Question is instead of replacing secondary why need to push. Most of solution I found that hide back button and keep on push and increasing navigation stack. Print this self.viewController(for: .secondary)?.navigationController?.viewControllers.count on segue/didSelectRow delegate. count keeps on increasing.