<TABLE> <S> <C>

<PAGE>
 
<ARTICLE> 9
<MULTIPLIER> 1,000
       
<S>                             <C>                     <C>
<PERIOD-TYPE>                   6-MOS                   6-MOS
<FISCAL-YEAR-END>                          DEC-31-1998             DEC-31-1997
<PERIOD-START>                             JAN-01-1998             JAN-01-1997
<PERIOD-END>                               JUN-30-1998             JUN-30-1997
<CASH>                                         205,789                 147,431
<INT-BEARING-DEPOSITS>                          19,140                  17,933
<FED-FUNDS-SOLD>                                17,088                  24,639
<TRADING-ASSETS>                                67,878                  34,059
<INVESTMENTS-HELD-FOR-SALE>                    687,151                 733,615
<INVESTMENTS-CARRYING>                       1,131,779                 882,584
<INVESTMENTS-MARKET>                         1,134,487                 869,030
<LOANS>                                      2,887,453               2,540,652
<ALLOWANCE>                                     45,050                  38,110
<TOTAL-ASSETS>                               5,200,617               4,521,583
<DEPOSITS>                                   3,415,788               2,997,545
<SHORT-TERM>                                   478,726                 757,331
<LIABILITIES-OTHER>                             81,370                  75,939
<LONG-TERM>                                    156,345                 156,158
<PREFERRED-MANDATORY>                                0                       0
<PREFERRED>                                          0                       0
<COMMON>                                       378,278                 332,924
<OTHER-SE>                                           0                       0
<TOTAL-LIABILITIES-AND-EQUITY>               5,200,617               4,521,583
<INTEREST-LOAN>                                123,036                 108,929
<INTEREST-INVEST>                               56,143                  52,248
<INTEREST-OTHER>                                 3,635                   1,679
<INTEREST-TOTAL>                               182,814                 162,856
<INTEREST-DEPOSIT>                              65,541                  59,180
<INTEREST-EXPENSE>                              90,890                  85,090
<INTEREST-INCOME-NET>                           91,924                  77,766
<LOAN-LOSSES>                                    3,497                   7,005
<SECURITIES-GAINS>                                  45                      29
<EXPENSE-OTHER>                                 68,989                  59,468
<INCOME-PRETAX>                                 61,391                  47,738
<INCOME-PRE-EXTRAORDINARY>                      61,391                  47,738
<EXTRAORDINARY>                                      0                       0
<CHANGES>                                            0                       0
<NET-INCOME>                                    40,494                  31,224
<EPS-PRIMARY>                                      .40                     .32
<EPS-DILUTED>                                      .40                     .31
<YIELD-ACTUAL>                                    4.21                    3.97
<LOANS-NON>                                        543                       0
<LOANS-PAST>                                     3,050                   4,196
<LOANS-TROUBLED>                                     0                       0
<LOANS-PROBLEM>                                    175                       0
<ALLOWANCE-OPEN>                                43,297                  35,514
<CHARGE-OFFS>                                    5,507                   6,554
<RECOVERIES>                                     2,522                   1,520
<ALLOWANCE-CLOSE>                               45,050                  38,110
<ALLOWANCE-DOMESTIC>                            45,050                  38,110
<ALLOWANCE-FOREIGN>                                  0                       0
<ALLOWANCE-UNALLOCATED>                              0                       0
        


</TABLE>