Quarterly Results Of Operations (Schedule Of Quarterly Results Of Operations) (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 Results Of Operations [Line Items]
Revenues	$ 188,477		$ 190,860		$ 176,570		$ 177,124		$ 171,646		$ 155,035		$ 136,994		$ 137,667		$ 733,031	$ 601,342	$ 566,251
Cost of sales	114,470		121,821		108,325		107,050		103,248		96,487		82,000		80,113		451,666	361,848	322,607
Gross profit	74,007		69,039		68,245		70,074		68,398		58,548		54,994		57,554
Operating income	41,588		38,723		41,349		40,032		36,840		31,776		30,428		30,595		161,692	129,639	138,713
Net income	$ 30,952		$ 29,657		$ 29,803		$ 28,797		$ 28,124		$ 23,263		$ 22,208		$ 21,672		$ 119,209	$ 95,267	$ 102,226
Basic	$ 0.77	[1]	$ 0.73	[1]	$ 0.74	[1]	$ 0.72	[1]	$ 0.70	[1]	$ 0.58	[1]	$ 0.55	[1]	$ 0.54	[1]	$ 2.96	$ 2.38	$ 2.57
Diluted	$ 0.76	[1]	$ 0.73	[1]	$ 0.74	[1]	$ 0.71	[1]	$ 0.70	[1]	$ 0.58	[1]	$ 0.55	[1]	$ 0.54	[1]	$ 2.94	$ 2.36	$ 2.55

[1] The sum of the quarterly per share amounts may not equal the annual amount reported, as per share amounts are computed independently for each quarter and for the full year.