Quarterly Results Of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 564,021	$ 586,221	$ 629,068	$ 592,172	$ 536,616	$ 604,244	$ 684,455	$ 650,492	$ 2,371,482	$ 2,475,807	$ 2,147,770
Gross profit	122,482	135,473	148,653	132,594	103,254	125,901	150,456	140,733	539,202	520,344	493,114
Income before income taxes	35,355	47,253	63,558	45,248	27,572	43,633	62,428	58,719	191,414	192,352	212,844
Net income	$ 28,807	$ 35,809	$ 47,527	$ 34,366	$ 20,179	$ 33,812	$ 47,224	$ 47,336	$ 146,509	$ 148,551	$ 132,884
Net income per common share:
Basic (in usd per share)	$ 1.15	$ 1.43	$ 1.90	$ 1.38	$ 0.80	$ 1.34	$ 1.87	$ 1.88	$ 5.86	$ 5.90	$ 5.31
Diluted (in usd per share)	1.14	1.42	1.89	1.38	0.80	1.33	1.86	1.86	5.84	5.83	$ 5.24
Stock market price, High (in usd per share)	109.79	95.52	97.77	86.13	80.89	102.23	104.90	132.30	109.79	132.30
Stock market price, Low (in usd per share)	87.15	92.93	75.59	64.70	59.68	98.40	80.95	99.46	64.70	59.68
Close (at end of quarter) (in usd per share)	$ 107.13	$ 91.85	$ 90.00	$ 76.82	$ 66.80	$ 69.35	$ 90.15	$ 104.15	$ 107.13	$ 66.80