Income Taxes Narrative (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Income Tax Contingency [Line Items]
Income Tax Effects Allocated Directly to Equity, Employee Stock Options	$ 200,000	$ 100,000	$ 1,100,000
Income Tax Effects Allocated to Equity from the Cancellation of Vested Stock Options and Valuation Difference on Restricted Stock	(400,000)
Income Tax Effects Allocated Directly to Equity, Cancellation of Vested Stock Options		(500,000)
Income Tax Effects Allocated Directly to Equity, Liabilities for Uncertain Tax Positions	(700,000)	200,000	200,000
Liabilities for uncertain tax positions - use of state net operating loss	(200,000)
Income Taxes Paid, Net of Refunds	92,900,000	77,200,000	68,900,000
Increase (Decrease) In Deferred Tax Liabilities Net, Adjustment to Purchase Accounting on Acquisitions	1,300,000
Income Tax Reconciliation, Nonqualified Stock Options and Disqualifying Dispositions of Incentive Stock Options	200,000	100,000
Unrecognized Tax Benefits	1,440,000	2,519,000	1,680,000	1,516,000
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	1,100,000	2,100,000	1,400,000
Accrued interest and penalties relating to net unrecognized tax benefits	200,000	400,000	300,000
Settlement With Taxing Authority [Member]
Income Tax Contingency [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Estimated Range of Change, Upper Bound	200,000
State [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards	$ 100,000