Fair Value Measurement (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 13,004	[1]	$ 6,018	[1]
Interest rate swap agreements	5,645	[2]	5,442	[2]
Aquisition-related contingent consideration	25,201		23,711		32,359	25,617
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	13,004	[1]	6,018	[1]
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swap agreements	5,645	[2]	5,442	[2]
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aquisition-related contingent consideration	$ 25,201		$ 23,711

[1] Consists of highly liquid investments with original maturities in excess of three months.

[2] Consists of interest rate swap agreements based on JIBAR and IBR whose value is determined using a pricing model with inputs that are observable in the market or can be derived principally from, or corroborated by, observable market data.