| **Long-Term Debt (Tables)**                                 | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
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| **Long-Term Debt [Abstract]**                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
| Schedule of Long-term Debt Instruments [Table Text Block]   |    2012 2011 2021 Notes (a)$ 325,000  325,000 2019 Notes (b)  425,000  425,000 Senior Credit Facility (c)  90,000  60,000 Rural Utility Service ("RUS") debt (d)  38,997  52,944 CoBank Mortgage ("CoBank") note payable (d)  797  1,344   Debt  879,794  864,288 Less unamortized discount paid on the 2019 Notes  2,743  3,016 Less current portion of long-term debt  1,928  3,241 Long-term debt, net$ 875,123  858,031 |
| Senior Note Redemption [Table Text Block]                   |   If redeemed during the twelve month period commencing June 1 of the year indicated: Redemption Price  2016 103.375%  2017 102.250%  2018 101.125%  2019 and thereafter 100.000%  If redeemed during the twelve month period commencing November 15 of the year indicated: Redemption Price  2014 104.313%  2015 102.875%  2016 101.438%  2017 and thereafter 100.000%                                                |
| Interest Margin [Table Text Block]                          |   Total Leverage Ratio (as defined) Applicable Margin  >3.75 4.00%  >3.25 but <3.75 3.50%  >2.75 but <3.25 3.00%  <2.75 2.50%                                                                                                                                                                                                                                                                                                                                                   |
| Schedule of Maturities of Long-term Debt [Table Text Block] |  Years ending December 31,   2013$1,928 2014 1,525 2015 91,387 2016 1,430 2017 1,475 2018 and thereafter 782,049   879,794 Less unamortized discount paid on 2019 Notes 2,743 Less current portion of long-term debt 1,928  $875,123                                                                                                                                                                                                                      |

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| - Definition
Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.
+ References
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| - Definition
Tabular disclosure of the combined aggregate amount of maturities and sinking fund requirements for all long-term borrowings for each of the five years following the date of the latest balance sheet date presented.
+ References
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