<TABLE> <S> <C>

<ARTICLE> 5
<MULTIPLIER> 1,000
       
<S>                                        <C>                     <C>                     <C>
<PERIOD-TYPE>                              3-MOS                   6-MOS                   9-MOS
<FISCAL-YEAR-END>                          DEC-31-1997             DEC-31-1997             DEC-31-1997
<PERIOD-END>                               MAR-31-1997             JUN-30-1997             SEP-30-1997
<CASH>                                          99,732                  77,173                  61,930
<SECURITIES>                                         0                       0                       0
<RECEIVABLES>                                   74,637                  83,890                  79,659
<ALLOWANCES>                                     2,842                   2,755                   2,654
<INVENTORY>                                      5,328                   5,721                   5,635
<CURRENT-ASSETS>                               190,225                 176,425                 163,944
<PP&E>                                         308,891                 316,954                 324,853
<DEPRECIATION>                                 155,220                 161,048                 166,663
<TOTAL-ASSETS>                                 691,098                 679,656                 673,061
<CURRENT-LIABILITIES>                           75,108                  57,307                  77,044
<BONDS>                                        235,410                 223,205                 186,705
<PREFERRED-MANDATORY>                                0                       0                       0
<PREFERRED>                                          0                       0                       0
<COMMON>                                           338                     338                     339  
<OTHER-SE>                                     445,511                 463,059                 475,474
<TOTAL-LIABILITY-AND-EQUITY>                   691,098                 679,656                 673,061
<SALES>                                        136,006                 287,404                 428,648
<TOTAL-REVENUES>                               136,006                 287,404                 428,648
<CGS>                                           51,527                 104,033                 157,939
<TOTAL-COSTS>                                   51,527                 104,033                 157,939
<OTHER-EXPENSES>                                 9,183                  18,420                  27,435
<LOSS-PROVISION>                                     0                       0                       0
<INTEREST-EXPENSE>                               4,525                   8,699                  12,553
<INCOME-PRETAX>                                 21,190                  54,161                  78,134
<INCOME-TAX>                                     8,695                  21,985                  31,735
<INCOME-CONTINUING>                             12,495                  32,176                  46,399
<DISCONTINUED>                                       0                       0                       0
<EXTRAORDINARY>                                      0                       0                       0
<CHANGES>                                            0                       0                       0
<NET-INCOME>                                    12,495                  32,176                  46,399
<EPS-PRIMARY>                                     0.57                    1.46                    2.10
<EPS-DILUTED>                                     0.56                    1.44                    2.07
        

</TABLE>