Consolidated Statements Of Income (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 [Abstract]
Net revenues	$ 172,420		$ 167,627		$ 156,985		$ 145,372		$ 144,900		$ 140,545		$ 130,649		$ 116,039		$ 642,404	[1]	$ 532,133	[1]	$ 419,006	[1]
Cost of revenues	99,802		100,893		100,200		94,560		89,278		84,881		79,083		66,800		395,455		320,042		215,154
Gross profit	72,618		66,734		56,785		50,812		55,622		55,664		51,566		49,239		246,949		212,091		203,852
Selling, general and administrative expenses	19,638		36,679		27,781		24,623		25,270		24,924		19,114		22,248		108,721		91,556		78,463
Income from operations	52,980		30,055		29,004		26,189		30,352		30,740		32,452		26,991		138,228		120,535		125,389
Other income, principally interest, net	2,534		1,632		5,923		6,119		4,008		4,876		1,959		2,283		16,208		13,126		10,059
Income before provision for income taxes	55,514		31,687		34,927		32,308		34,360		35,616		34,411		29,274		154,436		133,661		135,448
Income tax expense	11,554	[2]	5,480	[2]	7,287	[2]	7,259	[2]	4,597	[3]	5,177	[3]	6,151	[3]	4,143	[3]	31,580	[2]	20,068	[3]	16,953
Net income	$ 43,960		$ 26,207		$ 27,640		$ 25,049		$ 29,763		$ 30,439		$ 28,260		$ 25,131		$ 122,856		$ 113,593		$ 118,495
Dividend per share																	$ 0.24		$ 0.74		$ 0.24
EARNINGS PER SHARE:
Basic																	$ 2.95		$ 2.74		$ 2.86
Diluted	$ 1.05	[4]	$ 0.63	[4]	$ 0.66	[4]	$ 0.60	[4]	$ 0.71	[4]	$ 0.73	[4]	$ 0.68	[4]	$ 0.60	[4]	$ 2.94	[4]	$ 2.73	[4]	$ 2.86
Weighted average common shares outstanding:
Basic																	41,619		41,524		41,407
Diluted	41,736		41,724		41,696		41,711		41,679		41,618		41,580		41,566		41,717		41,611		41,491

[1] Net revenues are attributed to regions based upon customer location.

[2] The tax rate for the year ended December 31, 2011 was impacted by a favorable adjustment of $3.5 million as a result of the Company's review of its global uncertain tax liabilities provided on the "more likely than not" concept and other tax positions, which are based on the expiration of the statute of limitations related to certain global tax contingencies and the completion of certain tax audits. Out of the above, $3.2 million was reversed during the quarter and $0.9 million was reversed during the second quarter, offset by the charge of $0.6 million during the year; amounting to $0.3 million, $0.0 million and $0.3 million, for the first, second and third quarter respectively. The Company also reversed during the third quarter, $1.2 million based on the reconciliation of actual tax liability as per the tax returns and the tax provision as per the books. Further, a $0.6 million reversal of tax reserve was recorded during the third quarter, which had arisen on account of the reversal of a valuation allowance, created in the past, against deferred tax assets recognized on the allowance of doubtful accounts. During the fourth quarter ended December 31, 2011, the Company reviewed the filing requirements for certain USA State Income Tax returns. The Company updated the profit apportion method in those certain States. Accordingly, the Company provided $1.3 million, out of which $0.8 million relates to the prior years.

[3] The income tax provisions for the first quarter, third quarter and fourth quarter of 2010 were impacted by reversal of; provisions established for uncertain income tax positions liabilities and other tax positions of $0.33 million, $0.5 million as a result of the expiration of the statute of limitations related to certain global tax contingencies and completion of certain tax audits and provisions established for uncertain income tax positions liabilities and other tax positions of $0.45 million, respectively.

[4] Earnings per share for the quarter are computed independently and may not equal the earnings per share computed for the total year.