Summary Of Quarterly Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary Of Quarterly Data [Abstract]
Revenue	$ 442,996	$ 448,308	$ 466,569	$ 417,550	$ 399,685	$ 406,387	$ 413,343	$ 382,477	$ 1,775,423	$ 1,601,892	$ 1,485,807
Gross profit	240,626	246,730	260,543	227,537	217,695	224,274	232,757	215,544	975,436	890,270	816,116
Operating income	83,825	88,459	104,162	73,793	66,911	71,895	88,303	72,803	350,239	299,912	260,255
Net income attributable to stockholders	$ 52,369	$ 56,455	$ 67,202	$ 46,019	$ 44,349	$ 44,223	$ 56,912	$ 46,594	$ 222,045	$ 192,078	$ 181,906
Earnings per Share:
Basic	$ 0.59	$ 0.63	$ 0.75	$ 0.51	$ 0.49	$ 0.48	$ 0.61	$ 0.49	$ 2.47	$ 2.07	$ 1.82
Diluted	$ 0.58	$ 0.62	$ 0.74	$ 0.51	$ 0.48	$ 0.48	$ 0.60	$ 0.49	$ 2.44	$ 2.05	$ 1.79