Quarterly Financial Data (Schedule of Quarterly Data) (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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net sales	$ 257,700	$ 271,100	$ 273,900	$ 251,400	$ 251,600	$ 251,900	$ 255,400	$ 223,600	$ 226,700	$ 222,100	$ 215,600	$ 199,300	$ 1,054,132	$ 982,479	$ 863,717
Gross profit	96,600	104,100	105,200	91,800	87,900	92,400	91,700	77,700	77,500	79,600	63,200	76,000	397,701	349,749	296,283
Operating income													193,576	137,408	78,676
Net income attributable to the Company	$ 29,100	$ 40,000	$ 34,100	$ 29,200	$ 17,600	$ 27,700	$ 29,900	$ 7,700	$ 5,900	$ 15,300	$ 1,100	$ 10,800	$ 132,398	$ 82,891	$ 33,111
Basic earnings per share	$ 0.91	$ 1.24	$ 1.05	$ 0.90	$ 0.54	$ 0.86	$ 0.93	$ 0.24	$ 0.19	$ 0.47	$ 0.03	$ 0.34	$ 4.10	$ 2.57	$ 1.03
Diluted earnings per share	0.91	1.24	1.05	0.90	0.54	0.86	0.93	0.24	0.19	0.47	0.03	0.34	4.10	2.57	1.03
Cash dividends per share	0.19	0.18	0.18	0.18	0.18	0.17	0.17	0.17	0.17	0.17	0.17	0.17	$ 0.73	$ 0.69	$ 0.68
Maximum [Member]
Class A Common Stock prices:	90.30	91.51	82.91	78.45	78.31	81.40	65.45	67.30	65.25	57.60	53.40	49.05
Minimum [Member]
Class A Common Stock prices:	$ 75.92	$ 78.41	$ 69.29	$ 60.82	$ 58.41	$ 60.70	$ 58.35	$ 60.05	$ 56.45	$ 50.25	$ 43.90	$ 43.90