Quarterly Results of Operations (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 27, 2014	Jun. 28, 2014	Mar. 29, 2014	Dec. 31, 2013	Sep. 28, 2013	Jun. 29, 2013	Mar. 30, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Information [Line Items]
Sales	$ 104,153	$ 82,239	$ 82,060	$ 73,374	$ 89,895	$ 68,190	$ 68,329	$ 65,370	$ 341,826	$ 291,784	$ 273,395
Gross profit	57,273	46,041	45,517	40,083	49,321	38,821	36,926	36,825	188,914	161,893	149,619
Net income	$ 11,122	$ 11,223	$ 6,328	$ 4,976	$ 8,262	$ 5,042	$ 3,631	$ 4,574	$ 33,649	$ 21,509	$ 22,998
Net income per share:
Basic	$ 0.64	$ 0.65	$ 0.37	$ 0.29	$ 0.48	$ 0.29	$ 0.21	$ 0.27	$ 1.95	$ 1.26	$ 1.36
Diluted	$ 0.64	$ 0.64	$ 0.36	$ 0.29	$ 0.48	$ 0.29	$ 0.21	$ 0.27	$ 1.93	$ 1.25	$ 1.34