QUARTERLY FINANCIAL DATA - UNAUDITED (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
QUARTERLY FINANCIAL DATA - UNAUDITED
Net sales	$ 130,873	$ 132,976	$ 135,452	$ 135,703	$ 140,640	$ 137,699	$ 145,132	$ 131,632	$ 535,004	$ 555,103	$ 547,939
Net sales less cost of products sold (excluding depreciation and amortization)	43,987	48,172	50,838	48,485	50,448	47,593	49,879	44,169
Net income	$ 7,716	$ 12,106	$ 12,580	$ 11,061	$ 12,134	$ 12,224	$ 15,203	$ 9,809	$ 43,463	$ 49,370	$ 45,713
Basic:
Basic net income per common share (in dollars per share)	$ 0.15	$ 0.23	$ 0.24	$ 0.21	$ 0.23	$ 0.23	$ 0.29	$ 0.18	$ 0.84	$ 0.93	$ 0.85
Diluted:
Diluted net income per common share (in dollars per share)	$ 0.15	$ 0.23	$ 0.24	$ 0.21	$ 0.23	$ 0.23	$ 0.28	$ 0.18	$ 0.82	$ 0.92	$ 0.84
Average common shares outstanding
Basic (in shares)	50,970,000	51,891,000	52,314,000	52,451,000	52,773,000	52,857,000	52,942,000	53,608,000	51,902,408	53,042,253	53,897,834
Diluted (in shares)	51,710,000	52,634,000	53,179,000	53,330,000	53,649,000	53,759,000	53,845,000	54,525,000	52,708,898	53,940,812	54,671,029