Business Combinations (Narrative) (Details) (USD $)	3 Months Ended								3 Months Ended	12 Months Ended	3 Months Ended
	Mar. 31, 2012 Y	Mar. 31, 2011 Y	Mar. 31, 2012 Non-Compete Agreements [Member]	Mar. 31, 2011 Non-Compete Agreements [Member]	Mar. 31, 2012 Retail [Member]	Mar. 31, 2012 National Programs Divisions [Member]	Mar. 31, 2012 Wholesale Brokerage Divisions [Member]	Mar. 31, 2012 Services [Member]	Mar. 31, 2012 Prior To January 1, 2009 [Member]	Dec. 31, 2011 Prior To January 1, 2009 [Member]	Mar. 31, 2012 Subsequent To January 1, 2009 [Member]	Mar. 31, 2012 Purchased Customer Accounts [Member]	Mar. 31, 2011 Purchased Customer Accounts [Member]	Mar. 31, 2012 Stock Acquisitions [Member]	Mar. 31, 2012 Asset Acquisitions [Member]	Mar. 31, 2011 Asset Acquisitions [Member]	Mar. 31, 2012 Accounts Payable [Member]	Mar. 31, 2011 Accounts Payable [Member]	Mar. 31, 2012 Other Non-Current Liability [Member]	Mar. 31, 2011 Other Non-Current Liability [Member]
Business Acquisition [Line Items]
Number of acquisitions														1	2	13
Aggregate purchase price of acquisitions	$ 559,241,000	$ 54,128,000
Cash payments for acquisitions	401,247,000	43,855,000
Other Payable	21,391,000
Notes payable		550,000
Assumption of liabilities	131,889,000	782,000
Total goodwill	323,044,000	34,324,000
Goodwill related to the earn-out payables	4,714,000	8,941,000
Weighted average life (years)			5.0	5.0								15.0	15.0
Recorded earn-out payable	4,714,000	8,941,000
Average annual operating profit earned period, minimum (years)	1	1
Average annual operating profit earned period, maximum (years)	3	3
Goodwill currently deductible for income tax purposes	3,226,000	25,383,000
Goodwill currently non-deductible for income tax purposes	315,104,000
Goodwill assigned					2,088,000	253,901,000	811,000	66,244,000
Total revenues related to acquisitions	27,712,000	4,456,000
Income before income taxes related to acquisitions	362,000	972,000
Additional net consideration paid allocated to goodwill									2,907,000	99,000
Additional consideration paid in cash									2,907,000
Net additional consideration paid as note payable										99,000
Maximum future contingency payments related to acquisitions	136,763,000								2,483,000		134,280,000
Percentage recognition by acquirer of fair value of acquired assets	100.00%
Future earnings of acquired entities, term basis of potential earn-out obligations, minimum (years)											1
Future earnings of acquired entities, term basis of potential earn-out obligations, maximum (years)											3
Estimated acquisition earn-out payables	$ 51,908,000	$ 38,092,000															$ 8,782,000	$ 7,344,000	$ 43,126,000	$ 30,748,000