Debt (Details) In Thousands, unless otherwise specified	3 Months Ended			3 Months Ended
	Mar. 31, 2012 USD ($)	Mar. 31, 2012 EUR (€)	Dec. 31, 2011 USD ($)	Mar. 31, 2012 Amended Prudential Investment Management [Member] USD ($)	Mar. 31, 2012 JPMorgan Chase Bank, National Association [Member] USD ($)	Mar. 31, 2012 Series A Notes [Member] USD ($)	Mar. 31, 2012 Series B Notes [Member] USD ($)	Mar. 31, 2012 Long Term [Member] USD ($)	Dec. 31, 2011 Long Term [Member] USD ($)	Mar. 31, 2012 Long Term [Member] Bank Borrowings [Member] USD ($)	Dec. 31, 2011 Long Term [Member] Bank Borrowings [Member] USD ($)	Mar. 31, 2012 Long Term [Member] Credit Facility Borrowings [Member] USD ($)	Dec. 31, 2011 Long Term [Member] Credit Facility Borrowings [Member] USD ($)	Mar. 31, 2012 Long Term [Member] Notes Payable [Member] USD ($)	Dec. 31, 2011 Long Term [Member] Notes Payable [Member] USD ($)	Mar. 31, 2012 Long Term [Member] Collateralized Borrowings [Member] USD ($)	Dec. 31, 2011 Long Term [Member] Collateralized Borrowings [Member] USD ($)	Mar. 31, 2012 Long Term [Member] Capital Lease Obligations [Member] USD ($)	Dec. 31, 2011 Long Term [Member] Capital Lease Obligations [Member] USD ($)
Long-term Debt, Unclassified [Abstract]
Long-term debt, gross amount outstanding	$ 35,992		$ 36,455					$ 35,992	$ 36,455	$ 42	$ 49	$ 30,000	$ 30,000	$ 1,500	$ 1,500	$ 86	$ 127	$ 4,364	$ 4,779
Less: current portion	4,156		4,166
Long-term portion	31,836		32,289
Committed lines of credit	125,000
Debt Instrument, Face Amount						10,000	10,000
Debt Instrument, Interest Rate, Stated Percentage						4.00%	4.10%
Debt Instrument, Payment Terms						7 year term	10 year term
Debt Instrument, Maturity Date Range, Start						2014	2015
Debt Instrument, Maturity Date Range, End						2018	2021
Amount outstanding on notes payable to owners of acquired entity	1,500
Line of Credit Facility [Line Items]
Uncommitted lines of credit	82,669
Line of credit facility, Amount outstanding				20,000	10,000
Letters of credit, Outstanding amount	1,764
Bank guarantees	1,048
Commitment fees on unused lines of credit	79
Line of credit facility, Covenant restriction, Maximum Indebtedness to EBITDA					3.00 to 1
Line of credit facility, Covenant restriction, Minimum EBITDA to interest expense					3.50 to 1
Indebtedness to EBITDA ratio	0.54 to 1
EBITDA to interest expense ratio	28.73 to 1
Credit Facilities [Abstract]
Line of credit facility, Maximum borrowing capacity	2,669	2,000			125,000
Line of credit facility, Expiration date					May 5, 2016
Percentage stock of certain first tier foreign subsidiaries pledged as collateral under the credit agreement (in hundredths)					65.00%
Line of credit facility, Minimum commitment fee percentage (in hundredths)					0.25%
Line of credit facility, Maximum commitment fee percentage (in hundredths)					0.40%
Interest rate spread added to federal funds rate (in hundredths)					0.50%
Restriction on dividends and repurchases of common stock, Minimum				50,000	50,000
Restriction on dividends and repurchases of common stock, Maximum				75,000	75,000
Line of credit facility, weighted average interest rate at end of period (in hundredths)					1.77%
Amount of additional line of credit borrowing available					62,500
Line of credit facility, Expanded Maximum borrowing capacity					187,500
Sublimit on borrowings by foreign subsidiaries					100,000
Interest rate spread added to LIBOR rate for one month (in hundredths)					1.00%
Minimum interest rate spread added to LIBOR rate for one month based on leverage ratio (in hundredths)					0.50%
Maximum interest rate spread added to LIBOR rate for one month based on leverage ratio (in hundredths)					1.10%
Line of credit facility, Covenant restriction, Maximum leverage ratio restricting paying of dividends or repurchasing stock				2.00 to 1	2.00 to 1
Line of credit facility, Covenant restriction, Minimum leverage ratio restricting ability to make acquisitions				2.75 to 1	2.75 to 1
Line of credit facility, Covenant restriction, Maximum level that can be paid for acquisitions				$ 25,000	$ 25,000
Line of credit facility, Covenant restriction, Maximum leverage ratio under amended Private Shelf Agreement				3.00 to 1