<TABLE> <S> <C>

<PAGE>
 
<ARTICLE> 5
       
<S>                           <C>                  <C>                      <C>
<PERIOD-TYPE>                  12-MOS                12-MOS                   12-MOS
<FISCAL-YEAR-END>                 DEC-31-1998          DEC-31-1997               DEC-31-1996
<PERIOD-START>                    JAN-01-1998          JAN-01-1997                JAN-01-1996
<PERIOD-END>                      DEC-31-1998          DEC-31-1997                DEC-31-1996
<CASH>                                 10,953               14,061                     12,327
<SECURITIES>                          113,564              101,826                    101,065
<RECEIVABLES>                         100,545               67,855                     49,902
<ALLOWANCES>                          (1,200)              (1,268)                      (787)
<INVENTORY>                                 0                    0                          0
<CURRENT-ASSETS>                      233,579              197,193                    169,750
<PP&E>                                 68,332               55,649                     45,331
<DEPRECIATION>                         36,427               27,372                     23,098
<TOTAL-ASSETS>                        284,324              237,318                    202,322
<CURRENT-LIABILITIES>                  54,830               56,287                     37,850
<BONDS>                                     0                2,500                      2,600
<PREFERRED-MANDATORY>                       0                    0                          0
<PREFERRED>                                 0                    0                          0
<COMMON>                                  265                  260                        255
<OTHER-SE>                            220,241              176,344                    158,295
<TOTAL-LIABILITY-AND-EQUITY>          284,324              237,318                    202,322
<SALES>                               321,676              251,417                    206,879
<TOTAL-REVENUES>                      321,676              251,417                    206,879
<CGS>                                 163,054              130,424                     36,401
<TOTAL-COSTS>                         111,478              110,379                    184,253
<OTHER-EXPENSES>                            0                    0                          0
<LOSS-PROVISION>                          172                  481                        430
<INTEREST-EXPENSE>                        337                  197                        220
<INCOME-PRETAX>                        52,388               16,200                     27,508
<INCOME-TAX>                           22,160                8,238                     10,848
<INCOME-CONTINUING>                    30,228                7,962                     16,660
<DISCONTINUED>                              0                    0                          0
<EXTRAORDINARY>                             0                    0                          0
<CHANGES>                                   0                    0                          0
<NET-INCOME>                           30,228                7,962                     16,660
<EPS-PRIMARY>                            1.15                 0.31                       0.66
<EPS-DILUTED>                            1.11                 0.30                       0.64
        

</TABLE>