Revision To Previously Reported Financial Information (Correction Of Immaterial Error On Impacted Line Items Of The Consolidated Statements Of Income) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Consolidated Statements Of Income [Line Items]
Direct cost of revenues	$ 233,005	$ 249,975	$ 250,844	$ 223,084	$ 207,959	$ 206,831	$ 211,635	$ 199,174	$ 956,908	$ 825,599	$ 772,191
Selling, general and administrative expense	92,932	97,618	94,442	88,303	88,222	85,936	82,514	84,567	373,295	341,239	344,871
Special charges			15,212		21,775			29,356	15,212	51,131
Operating income	68,204	59,422	33,642	44,179	31,600	46,908	49,032	30,852	205,447	158,392	258,183
Income before income tax provision	54,604	45,589	22,065	30,869	15,620	32,370	37,513	21,888	153,127	107,391	221,668
Income tax provision	14,723	16,150	6,740	11,611	6,765	12,206	14,161	8,275	49,224	41,407	81,825
Net income	39,881	29,439	15,325	19,258	8,855	20,164	23,352	13,613	103,903	65,984	139,843
Earnings per common share - Basic	$ 1.00	$ 0.73	$ 0.38	$ 0.44	$ 0.20	$ 0.44	$ 0.51	$ 0.30	$ 2.53	$ 1.45	$ 2.80
Earnings per common share - Diluted	$ 0.93	$ 0.70	$ 0.36	$ 0.42	$ 0.19	$ 0.43	$ 0.48	$ 0.28	$ 2.39	$ 1.38	$ 2.63
Immaterial Error Correction [Member] | As Reported [Member]
Consolidated Statements Of Income [Line Items]
Direct cost of revenues										815,776	767,387
Selling, general and administrative expense										340,124	344,318
Special charges										52,020
Operating income										168,441	263,540
Income before income tax provision										117,440	227,025
Income tax provision										45,550	83,999
Net income										71,890	143,026
Earnings per common share - Basic										$ 1.58	$ 2.86
Earnings per common share - Diluted										$ 1.51	$ 2.70
Immaterial Error Correction [Member] | As Revised [Member]
Consolidated Statements Of Income [Line Items]
Direct cost of revenues										825,599	772,191
Selling, general and administrative expense										341,239	344,871
Special charges										51,131
Operating income										158,392	258,183
Income before income tax provision										107,391	221,668
Income tax provision										41,407	81,825
Net income										$ 65,984	$ 139,843
Earnings per common share - Basic										$ 1.45	$ 2.80
Earnings per common share - Diluted										$ 1.38	$ 2.63