Income Taxes (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 acquired_companies	Sep. 30, 2011	Dec. 31, 2011
Income Tax Disclosure [Abstract]
Percentage of income before taxes	25.40%	25.10%	33.40%	30.90%
Tax provision includes an out-of-period charge, related to write-offs of deferred tax assets			$ 491,000
Net operating losses, previously acquired companies			2
Tax benefits recognized due to settlements with taxing authorities			176,000
Tax benefits recognized due to lapse of statute of limitations	661,000		661,000
Liability for uncertain tax positions	11,500,000		11,500,000
Net liability, reduced for the federal effects of potential state tax exposures	8,100,000		8,100,000
Tax provision, included not yet reduced income tax payments	2,100,000		2,100,000
Long-term uncertain income tax positions within the next 12 months	6,000,000		6,000,000
Interest and penalties related to income tax	601,000		601,000		655,000
Deferred Tax Assets, Net, Current	22,900,000		22,900,000
Net long-term deferred tax assets	$ 9,100,000		$ 9,100,000