Financial Instruments (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
	Dec. 31, 2011	Jun. 30, 2012
Financial assets measured at fair value on a recurring basis
Cash equivalents (money market accounts and commercial paper investments)	111,775	50,337
Hedges of interest rate risk	(36)	(6)
Acquisition contingent consideration obligations	(1,197)	(1,197)
Fair value assets and liabilities measured on recurring basis, net	110,542	49,134
Hedges of interest rate risk [Member]
Valuation technique (approach)
Valuation Technique (Approach)	Market	Market
Acquisition contingent consideration obligations [Member]
Valuation technique (approach)
Valuation Technique (Approach)	Income	Income
Cash equivalents (money market accounts and commercial paper investments) [Member]
Valuation technique (approach)
Valuation Technique (Approach)	Market	Market
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Financial assets measured at fair value on a recurring basis
Cash equivalents (money market accounts and commercial paper investments)	111,775	50,337
Fair value assets and liabilities measured on recurring basis, net	111,775	50,337
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Financial assets measured at fair value on a recurring basis
Hedges of interest rate risk	(36)	(6)
Fair value assets and liabilities measured on recurring basis, net	(36)	(6)
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Financial assets measured at fair value on a recurring basis
Acquisition contingent consideration obligations	(1,197)	(1,197)
Fair value assets and liabilities measured on recurring basis, net	(1,197)	(1,197)