<TABLE> <S> <C>

<PAGE>
 
<ARTICLE> 7
       
<S>                             <C>                     <C>
<PERIOD-TYPE>                   9-MOS                   3-MOS
<FISCAL-YEAR-END>                          DEC-31-1998             DEC-31-1998
<PERIOD-START>                             JAN-01-1998             JUL-01-1998
<PERIOD-END>                               SEP-30-1998             SEP-30-1998
<DEBT-HELD-FOR-SALE>                       767,574,716                       0
<DEBT-CARRYING-VALUE>                        1,580,016                       0
<DEBT-MARKET-VALUE>                          1,692,016                       0
<EQUITIES>                                 112,631,795                       0
<MORTGAGE>                                     427,632                       0
<REAL-ESTATE>                                1,482,675                       0
<TOTAL-INVEST>                           1,075,178,800                       0
<CASH>                                         957,716                       0
<RECOVER-REINSURE>                           1,029,096                       0
<DEFERRED-ACQUISITION>                     110,155,962                       0
<TOTAL-ASSETS>                           1,218,864,566                       0
<POLICY-LOSSES>                            539,709,160                       0
<UNEARNED-PREMIUMS>                        107,934,360                       0
<POLICY-OTHER>                               9,243,350                       0
<POLICY-HOLDER-FUNDS>                        6,285,999                       0
<NOTES-PAYABLE>                             68,713,315                       0
<PREFERRED-MANDATORY>                                0                       0
<PREFERRED>                                          0                       0
<COMMON>                                    41,891,512                       0
<OTHER-SE>                                 367,417,273                       0
<TOTAL-LIABILITY-AND-EQUITY>             1,218,864,566                       0
<PREMIUMS>                                 292,818,529              98,732,729
<INVESTMENT-INCOME>                         47,069,340              16,243,369
<INVESTMENT-GAINS>                           3,898,774                (176,109)
<OTHER-INCOME>                               1,652,280                 564,415
<BENEFITS>                                 214,402,212              70,171,556
<UNDERWRITING-AMORTIZATION>                 43,648,744              14,737,385
<UNDERWRITING-OTHER>                        24,706,007               8,109,123
<INCOME-PRETAX>                             62,681,960              22,346,340
<INCOME-TAX>                                19,616,085               7,222,282
<INCOME-CONTINUING>                         43,065,875              15,124,058
<DISCONTINUED>                                       0                       0
<EXTRAORDINARY>                                      0                       0
<CHANGES>                                            0                       0
<NET-INCOME>                                43,065,875              15,124,058
<EPS-PRIMARY>                                     1.05                     .37
<EPS-DILUTED>                                     1.05                     .37
<RESERVE-OPEN>                             134,329,249                       0
<PROVISION-CURRENT>                        197,883,361                       0
<PROVISION-PRIOR>                           (6,930,844)                      0
<PAYMENTS-CURRENT>                         143,851,823                       0
<PAYMENTS-PRIOR>                            43,436,637                       0
<RESERVE-CLOSE>                            137,925,707                       0
<CUMULATIVE-DEFICIENCY>                              0                       0
        

</TABLE>