Operations by Business Segment and Geographic Information Geographic Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Revenues	$ 680,153	$ 646,034	$ 591,732
Long-Lived Assets	154,899	157,229	157,482
United States [Member]
Segment Reporting Information [Line Items]
Revenues	607,339	577,613	531,698
Long-Lived Assets	139,680	141,108	142,013
Canada [Member]
Segment Reporting Information [Line Items]
Revenues	72,814	68,421	60,034
Long-Lived Assets	$ 15,219	$ 16,121	$ 15,469