Segment Reporting Schedule of Revenues from External Customers and Long-Lived Assets (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net	$ 276,279	$ 273,163	$ 263,139	$ 260,927	$ 254,455	$ 245,428	$ 247,006	$ 234,191	$ 1,073,508	$ 981,080	$ 907,648
Property, Plant and Equipment, Net	138,824				125,418				138,824	125,418	115,295
Income Before Interest Expense and Taxes	87,917	84,596	81,869	79,037	75,868	75,380	72,126	73,906	333,419	297,280	250,754
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									507,239	505,200	470,600
Property, Plant and Equipment, Net	73,870				66,092				73,870	66,092	53,566
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									120,697	101,387	85,287
Property, Plant and Equipment, Net	17,195				17,263				17,195	17,263	20,113
Other Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue, Net									445,572	374,493	351,761
Property, Plant and Equipment, Net	$ 47,759				$ 42,063				$ 47,759	$ 42,063	$ 41,616