Supplemental Consolidated Balance Sheet Information (Narrative) (Details) (USD $)	3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Maximum [Member]	Nov. 01, 2012 Other Small Acquisitions [Member]	Dec. 31, 2011 Other Small Acquisitions [Member]
Other current and non-current assets - sign-on and retention bonuses	$ 19,200,000	$ 19,200,000
Other current and non-current assets - sign-on and retention bonuses issued		11,000,000	10,400,000
Depreciation expense		14,986,000	13,303,000	14,457,000
Other current and non-current liabilities - lease expiry		2022			2022
Other current and non-current assets - employee loans		seven
Other current and non-current assets - employee loans issued		11,400,000	6,000,000
Payments of Debt Issuance Costs			(2,814,000)
Disposals - fully depreciated assets		11,000,000
Property, Plant and Equipment, Transfers and Changes		1,600,000
Assets Held-for-sale, Long Lived	500,000	500,000
Capital Expenditures Incurred But Not Yet Paid		1,200,000
Capital Expenditures Paid		1,600,000
Other current liabilities - cash paid for defrred acquisition payments						2,600,000	2,900,000
Acquisition-related stock issuance and adjustment	2,600,000	2,551,000	6,012,000	7,340,000
Acquisition-related stock issuance and adjustment, shares	288,884
Deferred business acquisition obligations	10,863,000	10,863,000	11,732,000
Other current liabilities - Inforamtion Technology Build-Out		1,200,000
Contingent acquisition liability adjustment		1,065,000
Lease Obligations Maturity		2022			2022
Off-market Lease, Unfavorable	$ 1,900,000	$ 1,900,000