Unaudited Quarterly Financial Data Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	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, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Data [Abstract]
Net sales	$ 859,521	$ 990,264	$ 998,461	$ 834,202	$ 840,881	$ 881,012	$ 886,375	$ 757,700	$ 3,682,448	$ 3,365,968	$ 3,093,743
Gross profit	229,230	241,303	239,599	199,084	196,086	209,545	211,687	178,197	909,216	795,515	741,965
Net income	$ 28,116	$ 35,858	$ 40,405	$ 15,359	$ 17,642	$ 18,443	$ 17,596	$ 3,744	$ 119,738	$ 57,425	$ 30,880
Basic income (loss) per share
Net income (loss) per share (in dollars per share)	$ 0.42	$ 0.53	$ 0.60	$ 0.23	$ 0.26	$ 0.28	$ 0.26	$ 0.06	$ 1.78	$ 0.86	$ 0.47
Diluted income (loss) per share
Net income (loss) per share (in dollars per share)	$ 0.41	$ 0.53	$ 0.60	$ 0.23	$ 0.26	$ 0.27	$ 0.26	$ 0.06	$ 1.77	$ 0.85	$ 0.46