Quarterly Results of Operations (Unaudited) - Quarterly Results of Operations (Detail) - 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 Information Disclosure [Abstract]
Net sales	$ 27,400	$ 30,000	$ 32,400	$ 28,400	$ 25,100	$ 27,000	$ 30,000	$ 29,900	$ 118,217	$ 112,035	$ 108,920
Gross profit	7,900	9,600	11,200	9,500	7,400	8,200	9,500	9,700	38,271	34,825	35,167
Operating income	2,900	4,500	6,000	4,400	2,700	3,400	4,600	4,500	17,811	15,235	15,574
Net income	$ 2,700	$ 3,900	$ 5,000	$ 3,700	$ 4,300	$ 2,500	$ 3,300	$ 3,200	$ 15,325	$ 13,203	$ 10,457
Basic and diluted earnings per share	$ 0.22	$ 0.32	$ 0.40	$ 0.30	$ 0.34	$ 0.20	$ 0.27	$ 0.25	$ 1.23	$ 1.06	$ 0.84

The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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