<ARTICLE> 5
<MULTIPLIER> 1,000
       
                                                                                            

<PERIOD-TYPE>                   3-MOS                   3-MOS                   12-MOS                   12-MOS
12-MOS
<FISCAL-YEAR-END>                          DEC-31-1998             DEC-31-1998             DEC-31-1998             DEC-31-1998
             DEC-31-1998
<PERIOD-END>                               MAR-31-1998             MAR-31-1997             DEC-31-1997             DEC-31-1996
             DEC-31-1995
<CASH>                                           4,004                  10,081                   5,993                   5,557
                     755
<SECURITIES>                                         0                       0                       0                       0
                       0
<RECEIVABLES>                                   56,170                  48,114                  55,280                  48,546
                  34,062
<ALLOWANCES>                                     3,204                   3,867                   3,294                   3,773
                   3,311
<INVENTORY>                                          0                       0                       0                       0
                       0
<CURRENT-ASSETS>                                62,085                  60,665                  62,530                  55,475
                  35,175
<PP&E>                                         154,706                 132,082                 149,132                 125,727
                 103,959
<DEPRECIATION>                                 100,729                  88,759                  98,325                  85,506
                  69,542
<TOTAL-ASSETS>                                 199,645                 178,598                 192,434                 170,331
                 134,521
<CURRENT-LIABILITIES>                           43,539                  37,405                  44,612                  33,338
                  30,495
<BONDS>                                              0                       0                       0                       0
                       0
<PREFERRED-MANDATORY>                                0                       0                       0                       0
                       0
<PREFERRED>                                          0                       0                       0                       0
                       0
<COMMON>                                             0                       0                       0                       0
                       0
<OTHER-SE>                                     107,137                  98,022                 101,583                  99,353
                  70,874
<TOTAL-LIABILITY-AND-EQUITY>                   199,645                 178,598                 192,434                 170,331
                 134,521
<SALES>                                              0                       0                       0                       0
                       0
<TOTAL-REVENUES>                                96,064                  86,271                 358,594                 319,404
                 288,652
<CGS>                                                0                       0                       0                       0
                       0
<TOTAL-COSTS>                                   74,747                  64,361                 268,333                 237,443
                 219,084
<OTHER-EXPENSES>                                     0                       0                       0                       0
                       0
<LOSS-PROVISION>                                     0                       0                       0                       0
                       0
<INTEREST-EXPENSE>                                   0                       0                       0                       0
                       0
<INCOME-PRETAX>                                 24,502                  21,910                  90,261                  81,961
                  69,568
<INCOME-TAX>                                    10,256                   9,180                  37,786                  34,356
                  29,156
<INCOME-CONTINUING>                             14,246                  12,730                  52,475                  47,605
                  40,412
<DISCONTINUED>                                       0                       0                       0                       0
                       0
<EXTRAORDINARY>                                      0                       0                       0                       0
                       0
<CHANGES>                                            0                       0                       0                       0
                       0
<NET-INCOME>                                    14,246                  12,730                  52,475                  47,605
                  40,412
<EPS-PRIMARY>                                     0.09                    0.07                    0.32                    0.28
                    0.24
<EPS-DILUTED>                                     0.08                    0.07                    0.31                    0.28
                    0.24