Debt (Details) In Thousands, unless otherwise specified	12 Months Ended		12 Months Ended				12 Months Ended
	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2011 Amended Prudential Investment Management [Member] USD ($)	Dec. 31, 2011 JPMorgan Chase Bank, National Association [Member] USD ($)	Dec. 31, 2010 The Royak Bank of Scotland N.V. [Member] USD ($)	Dec. 31, 2010 The Royak Bank of Scotland N.V. [Member] EUR (€)	Dec. 31, 2011 Series A Notes [Member] USD ($)	Dec. 31, 2011 Series B Notes [Member] USD ($)	Dec. 31, 2011 Short Term [Member] Bank Borrowings [Member] USD ($)	Dec. 31, 2010 Short Term [Member] Bank Borrowings [Member] USD ($)	Dec. 31, 2011 Long Term [Member] USD ($)	Dec. 31, 2010 Long Term [Member] USD ($)	Dec. 31, 2011 Long Term [Member] Bank Borrowings [Member] USD ($)	Dec. 31, 2010 Long Term [Member] Bank Borrowings [Member] USD ($)	Dec. 31, 2011 Long Term [Member] Credit Facility Borrowings [Member] USD ($)	Dec. 31, 2010 Long Term [Member] Credit Facility Borrowings [Member] USD ($)	Dec. 31, 2011 Long Term [Member] Notes Payable [Member] USD ($)	Dec. 31, 2010 Long Term [Member] Notes Payable [Member] USD ($)	Dec. 31, 2011 Long Term [Member] Collateralized Borrowings [Member] USD ($)	Dec. 31, 2010 Long Term [Member] Collateralized Borrowings [Member] USD ($)	Dec. 31, 2011 Long Term [Member] Capital Lease Obligations [Member] USD ($)	Dec. 31, 2010 Long Term [Member] Capital Lease Obligations [Member] USD ($)
Short-term Debt [Abstract]
Bank borrowings									$ 0	$ 0
Long-term Debt, Unclassified [Abstract]
Long-term debt, gross amount outstanding	36,455										36,455	30,828	49	128	30,000	25,000	1,500	0	127	471	4,779	5,229
Less: current portion	4,166	3,154
Long-term portion	32,289	27,674
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	82,592
Line of credit facility, Amount outstanding			20,000	10,000
Letters of credit, Outstanding amount	1,759
Bank guarantees	1,015
Commitment fees on unused lines of credit	338
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				32.81 to 1
Credit Facilities [Abstract]
Line of credit facility, Maximum borrowing capacity				125,000	2,592	2,000
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)				1.75%
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	3.00 to 1
Aggregate maturities of outstanding debt including capital lease obligations [Abstract]
2012	5,354
2013	3,096
2014	3,211
2015	4,252
2016	13,994
Thereafter	11,995
Total minimum obligations	41,902
Less: amount representing interest	(5,447)
Total	$ 36,455										$ 36,455	$ 30,828	$ 49	$ 128	$ 30,000	$ 25,000	$ 1,500	$ 0	$ 127	$ 471	$ 4,779	$ 5,229