Fair Value Measurements (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012 interest_rate_swaps
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Fair value interest rate swap discount rate	1.60%
Assets transferred between Level 1 and Level 2	$ 0
Number of interest rate swaps to convert fixed interest rate on notes to floating rate	2
Revenue target period minimum (in years)	2 years
Revenue target period maximum (in years)	4 years
Percent change in projections affecting fair value of contigent consideration	5.00%
Increase in fair value of contingent consideration due to 5% increase in projections	20,000,000
Decrease in fair value of contigent considertion due to 5% decrease in projections	30,000,000
Senior Debt Obligations Due 2014 [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Fair value interest rate swap derivatives	$ 250,000,000
Debt instrument, maturity date	Dec. 31, 2014