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Geographic Information (Long-Lived Assets By Geographic Areas) (Details) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]      
Long-Lived Assets $ 948,114 $ 867,686 $ 775,837
United States [Member]      
Revenues from External Customers and Long-Lived Assets [Line Items]      
Long-Lived Assets 899,133 821,063 725,189
Canada [Member]      
Revenues from External Customers and Long-Lived Assets [Line Items]      
Long-Lived Assets 33,164 32,290 37,580
Other foreign countries [Member]      
Revenues from External Customers and Long-Lived Assets [Line Items]      
Long-Lived Assets $ 15,817 $ 14,333 $ 13,068