Summary Of Quarterly Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary Of Quarterly Data [Abstract]
Revenue	$ 506,121	$ 491,976	$ 508,940	$ 462,021	$ 442,996	$ 448,308	$ 466,569	$ 417,550	$ 1,969,058	$ 1,775,423	$ 1,601,892
Gross profit	272,474	274,002	292,715	258,191	240,626	246,730	260,543	227,537	1,097,382	975,436	890,270
Operating income	97,808	100,413	122,564	92,243	83,825	88,459	104,162	73,793	413,028	350,239	299,912
Net income attributable to stockholders	$ 38,257	$ 70,511	$ 85,357	$ 69,019	$ 52,369	$ 56,455	$ 67,202	$ 46,019	$ 263,144	$ 222,045	$ 192,078
Earnings per Share:
Basic	$ 0.44	$ 0.81	$ 0.97	$ 0.78	$ 0.59	$ 0.63	$ 0.75	$ 0.51	$ 3.00	$ 2.47	$ 2.07
Diluted	$ 0.43	$ 0.79	$ 0.95	$ 0.77	$ 0.58	$ 0.62	$ 0.74	$ 0.51	$ 2.94	$ 2.44	$ 2.05