<TABLE> <S> <C>

<PAGE>
 
<ARTICLE> 7
<MULTIPLIER> 1,000
       
<S>                             <C>                     <C>
<PERIOD-TYPE>                   12-MOS                   12-MOS
<FISCAL-YEAR-END>                          DEC-31-1997             DEC-31-1998
<PERIOD-START>                             JAN-01-1997             JAN-01-1998
<PERIOD-END>                               DEC-31-1997             DEC-31-1998
<DEBT-HELD-FOR-SALE>                           495,566                 457,219
<DEBT-CARRYING-VALUE>                                0                       0
<DEBT-MARKET-VALUE>                                  0                       0
<EQUITIES>                                      20,424                  21,099
<MORTGAGE>                                           0                       0
<REAL-ESTATE>                                        0                       0
<TOTAL-INVEST>                                 635,015                 609,347
<CASH>                                          21,801                  25,321
<RECOVER-REINSURE>                             136,640                 111,577
<DEFERRED-ACQUISITION>                         102,124                 100,957
<TOTAL-ASSETS>                               1,636,859               1,347,702
<POLICY-LOSSES>                                596,797                 504,911
<UNEARNED-PREMIUMS>                            365,052                 309,515
<POLICY-OTHER>                                       0                       0
<POLICY-HOLDER-FUNDS>                                0                       0
<NOTES-PAYABLE>                                198,602                 198,302
<PREFERRED-MANDATORY>                                0                       0
<PREFERRED>                                          0                       0
<COMMON>                                           190                     190
<OTHER-SE>                                     297,146                 165,962
<TOTAL-LIABILITY-AND-EQUITY>                 1,636,859               1,347,702
<PREMIUMS>                                     517,658                 509,693
<INVESTMENT-INCOME>                             35,960                  35,058
<INVESTMENT-GAINS>                               3,283                   3,272
<OTHER-INCOME>                                   2,094                   5,473
<BENEFITS>                                     298,638                 395,322
<UNDERWRITING-AMORTIZATION>                    132,984                 155,952
<UNDERWRITING-OTHER>                            38,913                  91,394
<INCOME-PRETAX>                                 65,026                (192,979)
<INCOME-TAX>                                    23,116                 (57,244)
<INCOME-CONTINUING>                             36,860                (141,184)
<DISCONTINUED>                                       0                       0
<EXTRAORDINARY>                                      0                       0
<CHANGES>                                            0                       0
<NET-INCOME>                                    36,860                (141,184)
<EPS-PRIMARY>                                     1.98                   (7.61)
<EPS-DILUTED>                                     1.93                   (7.61)
<RESERVE-OPEN>                                 251,783                 596,797
<PROVISION-CURRENT>                                  0                       0
<PROVISION-PRIOR>                                    0                       0
<PAYMENTS-CURRENT>                                   0                       0
<PAYMENTS-PRIOR>                                     0                       0
<RESERVE-CLOSE>                                596,797                 504,911
<CUMULATIVE-DEFICIENCY>                              0                       0
        

</TABLE>