<TABLE> <S> <C>

<PAGE>
 
<ARTICLE> 7
<MULTIPLIER> 1,000
       
<S>                             <C>                       <C>
<PERIOD-TYPE>                   3-MOS                     6-MOS
<FISCAL-YEAR-END>                          SEP-30-1997               SEP-30-1997
<PERIOD-START>                             JAN-01-1997               OCT-01-1996
<PERIOD-END>                               MAR-31-1997               MAR-31-1997
<DEBT-HELD-FOR-SALE>                           480,580                   480,580
<DEBT-CARRYING-VALUE>                                0                         0
<DEBT-MARKET-VALUE>                                  0                         0
<EQUITIES>                                           0                         0
<MORTGAGE>                                           0                         0
<REAL-ESTATE>                                        0                         0
<TOTAL-INVEST>                                 480,580                   480,580
<CASH>                                         148,377                   148,377
<RECOVER-REINSURE>                                   0                         0
<DEFERRED-ACQUISITION>                         108,123                   108,123
<TOTAL-ASSETS>                                 793,834                   793,834
<POLICY-LOSSES>                                 43,314                    43,314
<UNEARNED-PREMIUMS>                            112,650                   112,650
<POLICY-OTHER>                                       0                         0
<POLICY-HOLDER-FUNDS>                                0                         0
<NOTES-PAYABLE>                                      0                         0
<COMMON>                                        16,517                    16,517
<PREFERRED-MANDATORY>                                0                         0
<PREFERRED>                                      3,000                     3,000
<OTHER-SE>                                     426,088                   426,088
<TOTAL-LIABILITY-AND-EQUITY>                   793,834                   793,834
<PREMIUMS>                                      41,400                    84,523
<INVESTMENT-INCOME>                              8,143                    16,291
<INVESTMENT-GAINS>                                 392                       423
<OTHER-INCOME>                                       0                         0
<BENEFITS>                                       6,886                    17,723
<UNDERWRITING-AMORTIZATION>                      5,784                    12,899
<UNDERWRITING-OTHER>                             4,567                     9,870
<INCOME-PRETAX>                                 32,698                    60,745
<INCOME-TAX>                                         0                         0
<INCOME-CONTINUING>                             32,698                    60,745
<DISCONTINUED>                                       0                         0
<EXTRAORDINARY>                                      0                         0
<CHANGES>                                            0                         0
<NET-INCOME>                                    32,698                    60,745
<EPS-PRIMARY>                                     1.34                      2.50
<EPS-DILUTED>                                     1.34                      2.49
<RESERVE-OPEN>                                  45,981                    49,875
<PROVISION-CURRENT>                              3,604                     7,997
<PROVISION-PRIOR>                                3,275                     9,719
<PAYMENTS-CURRENT>                             (2,129)                   (2,560)
<PAYMENTS-PRIOR>                               (7,417)                  (21,717)
<RESERVE-CLOSE>                                 43,314                    43,314
<CUMULATIVE-DEFICIENCY>                              0                         0
        


</TABLE>