Guarantor Subsidiaries (Schedule Of Guarantor Subsidiaries - Balance Sheet) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	$ 113,047	$ 69,531	$ 59,966	$ 38,081
Accounts receivable, including intercompany	76,356	93,333
Inventories	6,156	7,058
Current deferred income taxes	19,322	13,659
Prepaid income taxes	4,911	2,643
Prepaid expenses	13,518	11,447
Total current assets	233,310	197,671
Investments of deferred compensation plans	40,583	36,089
Properties and equipment, at cost, less accumulated depreciation	90,229	91,934
Identifiable intangible assets less accumulated amortization	57,348	57,177
Goodwill	466,271	465,832
Other assets	11,137	10,923
Total Assets	898,878	859,626
Accounts Payable, including intercompany	35,921	48,472
Current portion of long-term debt	179,154
Income taxes	4,561	4,938
Accrued insurance	42,616	40,654
Accrued compensation	42,156	45,457
Other current liabilities	33,840	17,301
Total current liabilities	338,248	156,822
Deferred income taxes	27,981	27,662
Long-term debt		174,890
Deferred compensation liabilities	39,660	35,599
Other liabilities	11,702	11,362
Stockholders' equity	481,287	453,291
Total Liabilities and Stockholders' Equity	898,878	859,626
Parent [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	113,927	56,342	53,280	32,470
Accounts receivable, including intercompany	1,005	925
Prepaid income taxes	6,494	4,043
Prepaid expenses	1,652	564
Total current assets	123,078	61,874
Properties and equipment, at cost, less accumulated depreciation	10,584	10,984
Other assets	18,049	19,025
Investments in subsidiaries	908,756	874,692
Total Assets	1,060,467	966,575
Accounts Payable, including intercompany	385,095	325,916
Current portion of long-term debt	179,154
Income taxes	3,776	1,019
Accrued insurance	1,581	1,339
Accrued compensation	2,128	4,119
Other current liabilities	4,297	2,786
Total current liabilities	576,031	335,179
Long-term debt		174,890
Other liabilities	3,149	3,215
Stockholders' equity	481,287	453,291
Total Liabilities and Stockholders' Equity	1,060,467	966,575
Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	(9,574)	4,674	(803)	(1,422)
Accounts receivable, including intercompany	466,915	427,341
Inventories	5,553	6,505
Current deferred income taxes	21,462	14,633
Prepaid income taxes	327
Prepaid expenses	11,676	10,656
Total current assets	496,359	463,809
Properties and equipment, at cost, less accumulated depreciation	76,963	78,236
Identifiable intangible assets less accumulated amortization	57,348	57,177
Goodwill	461,801	461,277
Other assets	1,757	2,005
Investments in subsidiaries	25,726	24,298
Total Assets	1,119,954	1,086,802
Accounts Payable, including intercompany	37,026	53,934
Income taxes	1,205	3,816
Accrued insurance	41,035	39,315
Accrued compensation	39,631	40,891
Other current liabilities	31,596	13,903
Total current liabilities	150,493	151,859
Deferred income taxes	51,580	51,566
Other liabilities	7,639	7,352
Stockholders' equity	910,242	876,025
Total Liabilities and Stockholders' Equity	1,119,954	1,086,802
Non-Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	8,694	8,515	7,489	7,033
Accounts receivable, including intercompany	1,076	889
Inventories	603	553
Current deferred income taxes	267	173
Prepaid expenses	190	227
Total current assets	10,830	10,357
Investments of deferred compensation plans	40,583	36,089
Properties and equipment, at cost, less accumulated depreciation	2,682	2,714
Goodwill	4,470	4,555
Other assets	14,930	13,797
Total Assets	73,495	67,512
Accounts Payable, including intercompany	6,440	4,444
Income taxes	1,490	1,503
Accrued compensation	397	447
Other current liabilities	354	1,759
Total current liabilities	8,681	8,153
Deferred compensation liabilities	39,660	35,599
Other liabilities	914	795
Stockholders' equity	24,240	22,965
Total Liabilities and Stockholders' Equity	73,495	67,512
Consolidating Adjustments [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Accounts receivable, including intercompany	(392,640)	(335,822)
Current deferred income taxes	(2,407)	(1,147)
Prepaid income taxes	(1,910)	(1,400)
Total current assets	(396,957)	(338,369)
Other assets	(23,599)	(23,904)
Investments in subsidiaries	(934,482)	(898,990)
Total Assets	(1,355,038)	(1,261,263)
Accounts Payable, including intercompany	(392,640)	(335,822)
Income taxes	(1,910)	(1,400)
Other current liabilities	(2,407)	(1,147)
Total current liabilities	(396,957)	(338,369)
Deferred income taxes	(23,599)	(23,904)
Stockholders' equity	(934,482)	(898,990)
Total Liabilities and Stockholders' Equity	$ (1,355,038)	$ (1,261,263)