An excess insurer may not challenge an underlying insurer’s payment decision as outside the scope of coverage and thus as improperly eroding the primary insurer’s coverage and prematurely triggering the excess insurer’s coverage—unless there is an indication that the payments were motivated by fraud or bad faith or the excess policy contains specific language reserving the excess insurer’s right to challenge the primary insurers’ payments.  An ordinary insured would not expect that it would have to defend its primary insurer’s decision to pay claims.