Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Jurisdiction	Jun. 30, 2011
Income Taxes
Effective tax rate (as a percent)	26.80%	27.60%	26.80%	27.50%
Minimum number of tax jurisdictions			60
Liability for unrecognized tax benefits, including penalties and interest, which if recognized would impact the effective tax rate	$ 23,037		$ 23,037
Unrecognized tax benefits, anticipated adjustment for changing facts and circumstances, over the next twelve month period	7,000		7,000
Gain on adjustment of a contingent acquisition related purchase price obligation		17,813		17,813
One-time tax cost related to gain on adjustment of a contingent acquisition related purchase price obligation		$ 6,600
Effective tax rate, excluding the effect of one-time tax cost (as a percent)		26.70%		27.10%