Quarterly Results of Operations (Unaudited) (Results of Operations) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 210,672	$ 201,944	$ 191,157	$ 198,810	$ 193,768	$ 221,842	$ 242,852	$ 239,798	$ 802,583	$ 898,260	$ 879,091
Gross margin	80,703	75,518	69,969	65,630	64,203	78,867	85,828	85,394	$ 291,820	$ 314,292	$ 310,783
Net income (loss)	$ 15,205	$ 7,006	$ 14,520	$ 13,259	$ (28,760)	$ 23,387	$ 24,293	$ 28,399
Net income (loss) per share:
Basic (in dollars per share)	$ 0.82	$ 0.37	$ 0.78	$ 0.71	$ (1.55)	$ 1.26	$ 1.31	$ 1.53
Diluted (in dollars per share)	$ 0.81	$ 0.37	$ 0.78	$ 0.71	$ (1.55)	$ 1.25	$ 1.30	$ 1.52