Guarantor Subsidiaries (Schedule Of Guarantor Subsidiaries - Balance Sheet) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	$ 83,204	$ 69,531	$ 69,296	$ 38,081
Accounts receivable, including intercompany	80,117	93,333
Inventories	6,729	7,058
Current deferred income taxes	25,101	13,659
Prepaid income taxes	3,538	2,643
Prepaid expenses	17,684	11,447
Total current assets	216,373	197,671
Investments of deferred compensation plans	40,683	36,089
Properties and equipment, at cost, less accumulated depreciation	89,800	91,934
Identifiable intangible assets less accumulated amortization	56,979	57,177
Goodwill	466,940	465,832
Other assets	10,765	10,923
Total Assets	881,540	859,626
Accounts payable, including intercompany	44,523	48,472
Current portion of long-term debt	181,340
Income taxes	5,529	4,938
Accrued insurance	41,737	40,654
Accrued compensation	46,689	45,457
Other current liabilities	56,536	17,301
Total current liabilities	376,354	156,822
Deferred income taxes	27,454	27,662
Long-term debt		174,890
Deferred compensation liabilities	39,406	35,599
Other liabilities	11,499	11,362
Stockholders' equity	426,827	453,291
Total Liabilities and Stockholders' Equity	881,540	859,626
Parent [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	84,842	56,342	58,449	32,470
Accounts receivable, including intercompany	960	925
Prepaid income taxes	6,583	4,043
Prepaid expenses	7,199	564
Total current assets	99,584	61,874
Properties and equipment, at cost, less accumulated depreciation	10,361	10,984
Other assets	18,155	19,025
Investments in subsidiaries	924,423	874,692
Total Assets	1,052,523	966,575
Accounts payable, including intercompany	421,662	325,916
Current portion of long-term debt	181,340
Income taxes	5,034	1,019
Accrued insurance	153	1,339
Accrued compensation	3,226	4,119
Other current liabilities	11,023	2,786
Total current liabilities	622,438	335,179
Long-term debt		174,890
Other liabilities	3,258	3,215
Stockholders' equity	426,827	453,291
Total Liabilities and Stockholders' Equity	1,052,523	966,575
Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	(10,511)	4,674	3,010	(1,422)
Accounts receivable, including intercompany	496,001	427,341
Inventories	6,175	6,505
Current deferred income taxes	27,237	14,633
Prepaid expenses	10,245	10,656
Total current assets	529,147	463,809
Properties and equipment, at cost, less accumulated depreciation	76,957	78,236
Identifiable intangible assets less accumulated amortization	56,979	57,177
Goodwill	462,489	461,277
Other assets	1,770	2,005
Investments in subsidiaries	27,629	24,298
Total Assets	1,154,971	1,086,802
Accounts payable, including intercompany	35,005	53,934
Income taxes	3,349	3,816
Accrued insurance	41,584	39,315
Accrued compensation	43,131	40,891
Other current liabilities	47,646	13,903
Total current liabilities	170,715	151,859
Deferred income taxes	51,791	51,566
Other liabilities	7,265	7,352
Stockholders' equity	925,200	876,025
Total Liabilities and Stockholders' Equity	1,154,971	1,086,802
Non-Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	8,873	8,515	7,837	7,033
Accounts receivable, including intercompany	741	889
Inventories	554	553
Current deferred income taxes	177	173
Prepaid income taxes	218
Prepaid expenses	240	227
Total current assets	10,803	10,357
Investments of deferred compensation plans	40,683	36,089
Properties and equipment, at cost, less accumulated depreciation	2,482	2,714
Goodwill	4,451	4,555
Other assets	15,177	13,797
Total Assets	73,596	67,512
Accounts payable, including intercompany	5,441	4,444
Income taxes	409	1,503
Accrued compensation	332	447
Other current liabilities	180	1,759
Total current liabilities	6,362	8,153
Deferred compensation liabilities	39,406	35,599
Other liabilities	976	795
Stockholders' equity	26,852	22,965
Total Liabilities and Stockholders' Equity	73,596	67,512
Consolidating Adjustments [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Accounts receivable, including intercompany	(417,585)	(335,822)
Current deferred income taxes	(2,313)	(1,147)
Prepaid income taxes	(3,263)	(1,400)
Total current assets	(423,161)	(338,369)
Other assets	(24,337)	(23,904)
Investments in subsidiaries	(952,052)	(898,990)
Total Assets	(1,399,550)	(1,261,263)
Accounts payable, including intercompany	(417,585)	(335,822)
Income taxes	(3,263)	(1,400)
Other current liabilities	(2,313)	(1,147)
Total current liabilities	(423,161)	(338,369)
Deferred income taxes	(24,337)	(23,904)
Stockholders' equity	(952,052)	(898,990)
Total Liabilities and Stockholders' Equity	$ (1,399,550)	$ (1,261,263)