Guarantor Subsidiaries (Schedule Of Guarantor Subsidiaries - Income Statement) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Guarantor Subsidairies [Line Items]
Service Revenues and Sales	$ 354,353	$ 341,439	$ 1,061,466	$ 1,005,717
Cost of services provided and goods sold	256,610	245,063	771,423	722,118
Selling, general and administrative expenses	52,955	47,618	155,892	153,696
Depreciation	6,557	6,313	19,178	18,959
Amortization	1,135	1,134	3,375	3,243
Other operating expenses	1,126		1,126
Total costs and expenses	318,383	300,128	950,994	898,016
Income/ (loss) from operations	35,970	41,311	110,472	107,701
Interest expense	(3,743)	(3,555)	(11,032)	(10,260)
Other (expense)/income - net	1,840	(1,935)	2,965	881
Income before income taxes	34,067	35,821	102,405	98,322
Income tax (provision)/ benefit	(13,222)	(13,934)	(39,841)	(38,048)
Net income	20,845	21,887	62,564	60,274
Parent [Member]
Guarantor Subsidairies [Line Items]
Selling, general and administrative expenses	5,991	5,678	17,124	17,936
Depreciation	237	235	704	711
Amortization	486	467	1,437	1,287
Total costs and expenses	6,714	6,380	19,265	19,934
Income/ (loss) from operations	(6,714)	(6,380)	(19,265)	(19,934)
Interest expense	(3,517)	(3,361)	(10,437)	(9,814)
Other (expense)/income - net	4,450	4,379	13,196	12,011
Income before income taxes	(5,781)	(5,362)	(16,506)	(17,737)
Income tax (provision)/ benefit	1,877	1,677	5,376	5,863
Equity in net income of subsidiaries	24,749	25,572	73,694	72,148
Net income	20,845	21,887	62,564	60,274
Guarantor Subsidiaries [Member]
Guarantor Subsidairies [Line Items]
Service Revenues and Sales	347,384	334,937	1,040,015	985,500
Cost of services provided and goods sold	252,688	241,604	759,549	711,335
Selling, general and administrative expenses	43,992	42,595	131,695	130,617
Depreciation	6,099	5,870	17,816	17,651
Amortization	649	667	1,938	1,956
Other operating expenses	1,126		1,126
Total costs and expenses	304,554	290,736	912,124	861,559
Income/ (loss) from operations	42,830	44,201	127,891	123,941
Interest expense	(211)	(194)	(551)	(446)
Other (expense)/income - net	(4,184)	(4,301)	(12,982)	(11,918)
Income before income taxes	38,435	39,706	114,358	111,577
Income tax (provision)/ benefit	(14,560)	(15,029)	(43,442)	(42,164)
Equity in net income of subsidiaries	885	953	2,857	2,861
Net income	24,760	25,630	73,773	72,274
Non-Guarantor Subsidiaries [Member]
Guarantor Subsidairies [Line Items]
Service Revenues and Sales	6,969	6,502	21,451	20,217
Cost of services provided and goods sold	3,922	3,459	11,874	10,783
Selling, general and administrative expenses	2,972	(655)	7,073	5,143
Depreciation	221	208	658	597
Total costs and expenses	7,115	3,012	19,605	16,523
Income/ (loss) from operations	(146)	3,490	1,846	3,694
Interest expense	(15)		(44)
Other (expense)/income - net	1,574	(2,013)	2,751	788
Income before income taxes	1,413	1,477	4,553	4,482
Income tax (provision)/ benefit	(539)	(582)	(1,775)	(1,747)
Net income	874	895	2,778	2,735
Consolidating Adjustments [Member]
Guarantor Subsidairies [Line Items]
Equity in net income of subsidiaries	(25,634)	(26,525)	(76,551)	(75,009)
Net income	$ (25,634)	$ (26,525)	$ (76,551)	$ (75,009)