Annual report pursuant to Section 13 and 15(d)

Industry Segments Data (Reconciliation of reportable segment revenues) (Details)

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Industry Segments Data (Reconciliation of reportable segment revenues) (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 12 Months Ended
Dec. 31, 2012
Sep. 30, 2012
Jun. 30, 2012
Mar. 31, 2012
Dec. 31, 2011
Sep. 30, 2011
Jun. 30, 2011
Mar. 31, 2011
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Reconciliation from Segment Totals to Consolidated [Abstract]                      
Reportable Segment Revenues                 $ 716,446 $ 685,698 $ 656,868
Less intersegment revenues eliminated in consolidation                 6,265 6,317 5,618
External revenues $ 183,676 $ 178,494 $ 176,104 $ 171,907 $ 168,812 $ 177,703 $ 168,089 $ 164,777 $ 710,181 $ 679,381 $ 651,250