Income Taxes (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Income Taxes [Line Items]
Provision for income taxes	$ 14,765,000	$ 18,612,000	$ 60,248,000	$ 55,722,000
Effective tax rate	23.40%	32.60%	29.10%	32.50%
Minimum [Member]
Income Taxes [Line Items]
Change in unrecognized tax benefits over next 12 months	0		0
Maximum [Member]
Income Taxes [Line Items]
Change in unrecognized tax benefits over next 12 months	$ 3,100,000		$ 3,100,000