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Operations by Business Segment and Geographic Information Geographic Information (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Segment Reporting Information [Line Items]      
Revenues $ 789,911us-gaap_Revenues $ 713,848us-gaap_Revenues $ 680,153us-gaap_Revenues
Long-lived assets, net 213,808us-gaap_NoncurrentAssets 181,362us-gaap_NoncurrentAssets 169,183us-gaap_NoncurrentAssets
United States [Member]      
Segment Reporting Information [Line Items]      
Revenues 706,145us-gaap_Revenues
/ us-gaap_StatementGeographicalAxis
= country_US		 637,524us-gaap_Revenues
/ us-gaap_StatementGeographicalAxis
= country_US		 607,339us-gaap_Revenues
/ us-gaap_StatementGeographicalAxis
= country_US
Long-lived assets, net 196,116us-gaap_NoncurrentAssets
/ us-gaap_StatementGeographicalAxis
= country_US		 166,598us-gaap_NoncurrentAssets
/ us-gaap_StatementGeographicalAxis
= country_US		 153,946us-gaap_NoncurrentAssets
/ us-gaap_StatementGeographicalAxis
= country_US
Canada [Member]      
Segment Reporting Information [Line Items]      
Revenues 83,766us-gaap_Revenues
/ us-gaap_StatementGeographicalAxis
= country_CA		 76,324us-gaap_Revenues
/ us-gaap_StatementGeographicalAxis
= country_CA		 72,814us-gaap_Revenues
/ us-gaap_StatementGeographicalAxis
= country_CA
Long-lived assets, net $ 17,692us-gaap_NoncurrentAssets
/ us-gaap_StatementGeographicalAxis
= country_CA		 $ 14,764us-gaap_NoncurrentAssets
/ us-gaap_StatementGeographicalAxis
= country_CA		 $ 15,237us-gaap_NoncurrentAssets
/ us-gaap_StatementGeographicalAxis
= country_CA