Selected Quarterly Financial Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Quarterly Financial Data [Line Items]
Net revenues	$ 187,773		$ 186,407		$ 178,979		$ 170,744		$ 172,420		$ 167,627		$ 156,985		$ 145,372		$ 723,903	[1]	$ 642,404	[1]	$ 532,133	[1]
Cost of revenues	102,918		101,588		105,121		99,292		99,802		100,893		100,200		94,560		408,919		395,455		320,042
Gross profit	84,855		84,819		73,858		71,452		72,618		66,734		56,785		50,812		314,984		246,949		212,091
Selling, general and administrative expenses	28,131		29,036		18,931		26,946		19,638		36,679		27,781		24,623		103,044		108,721		91,556
Income from operations	56,724		55,783		54,927		44,506		52,980		30,055		29,004		26,189		211,940		138,228		120,535
Other income net	7,280		9,964		2,455		8,289		2,534		1,632		5,923		6,119		27,988		16,208		13,126
Income before income taxes	64,004		65,747		57,382		52,795		55,514		31,687		34,927		32,308		239,928		154,436		133,661
Income tax expense	14,077	[2]	14,265	[2]	13,993	[2]	12,050	[2]	11,554	[3]	5,480	[3]	7,287	[3]	7,259	[3]	54,385	[2]	31,580	[3]	20,068
Net income	$ 49,927		$ 51,482		$ 43,389		$ 40,745		$ 43,960		$ 26,207		$ 27,640		$ 25,049		$ 185,543		$ 122,856		$ 113,593
Earnings per share, diluted	$ 1.19	[4]	$ 1.23	[4]	$ 1.04	[4]	$ 0.98	[4]	$ 1.05	[4]	$ 0.63	[4]	$ 0.66	[4]	$ 0.60	[4]	$ 4.44	[4]	$ 2.94	[4]	$ 2.73
Weighted average shares outstanding, diluted	41,833		41,802		41,774		41,765		41,736		41,724		41,696		41,711		41,793		41,717		41,611

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

[2] The tax rate for the year ended December 31, 2012 was impacted by a favorable adjustment of $0.24 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 is based on the completion of certain tax Appeals. Without the above, the effective tax rate for the year ended December 31, 2012 was 22.8%.

[3] 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 fourth 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 U.S. 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.

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