<ARTICLE> 5
<MULTIPLIER> 1,000
       
                                                  
<PERIOD-TYPE>                   3-MOS                   3-MOS
<FISCAL-YEAR-END>                          DEC-31-1998             DEC-31-1997
<PERIOD-END>                               MAR-31-1998             MAR-31-1997
<CASH>                                          84,252                  99,732
<SECURITIES>                                         0                       0
<RECEIVABLES>                                   77,736                  74,637
<ALLOWANCES>                                     2,524                   2,842
<INVENTORY>                                      3,670                   5,328
<CURRENT-ASSETS>                               181,066                 190,225
<PP&E>                                         340,600                 308,891
<DEPRECIATION>                                 176,500                 155,220
<TOTAL-ASSETS>                                 689,929                 691,098
<CURRENT-LIABILITIES>                           72,458                  75,108
<BONDS>                                        172,705                 235,410
<PREFERRED-MANDATORY>                                0                       0
<PREFERRED>                                          0                       0
<COMMON>                                           340                     338
<OTHER-SE>                                     507,613                 445,511
<TOTAL-LIABILITY-AND-EQUITY>                   689,929                 691,098
<SALES>                                        143,399                 136,006
<TOTAL-REVENUES>                               143,399                 136,006
<CGS>                                           55,423                  51,527
<TOTAL-COSTS>                                   55,423                  51,527
<OTHER-EXPENSES>                                 8,930                   9,183
<LOSS-PROVISION>                                     0                       0
<INTEREST-EXPENSE>                               3,462                   4,525
<INCOME-PRETAX>                                 23,607                  21,190
<INCOME-TAX>                                     9,642                   8,695
<INCOME-CONTINUING>                             13,965                  12,495
<DISCONTINUED>                                       0                       0
<EXTRAORDINARY>                                      0                       0
<CHANGES>                                            0                       0
<NET-INCOME>                                    13,965                  12,495
<EPS-PRIMARY>                                     0.63                    0.57
<EPS-DILUTED>                                     0.62                    0.56