Quarterly financial data - Schedule of Quarterly Financial Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Interim Reporting [Line Items]
Net Sales	$ 112,035	$ 114,752	$ 119,492	$ 116,041	$ 123,085	$ 117,306	$ 116,670	$ 113,060	$ 462,320	$ 470,121	$ 460,629
Gross profit	93,531	92,379	95,816	94,102	99,846	93,452	93,484	90,720	375,828	377,502	370,168
Net income (loss) from continuing operations, net of tax	14,636	13,118	13,967	12,215	11,530	12,951	10,519	(36,740)	53,936	(1,740)	27,758
Net income (loss) from discontinued operations, net of tax	5,878	(5,558)	(2,762)	(199)	862	(573)	(561)	939	(2,641)	667	16,450
Net income (loss)	$ 20,514	$ 7,560	$ 11,205	$ 12,016	$ 12,392	$ 12,378	$ 9,958	$ (35,801)	$ 51,295	$ (1,073)	$ 44,208
Net income (loss) from continuing operations, net of tax	$ 0.76	$ 0.69	$ 0.74	$ 0.65	$ 0.62	$ 0.70	$ 0.58	$ (2.05)	$ 2.84	$ (0.10)	$ 1.58
Net income (loss) from discontinued operations, net of tax	$ 0.30	$ (0.29)	$ (0.15)	$ (0.01)	$ 0.05	$ (0.03)	$ (0.03)	$ 0.05	$ (0.14)	$ 0.04	$ 0.93
Net income (loss)	$ 1.06	$ 0.40	$ 0.59	$ 0.64	$ 0.67	$ 0.67	$ 0.55	$ (2.00)	$ 2.70	$ (0.06)	$ 2.51
Net income (loss) from continuing operations, net of tax	$ 0.74	$ 0.67	$ 0.73	$ 0.64	$ 0.62	$ 0.69	$ 0.57	$ (2.05)	$ 2.78	$ (0.10)	$ 1.55
Net income (loss) from discontinued operations, net of tax	$ 0.30	$ (0.28)	$ (0.15)	$ (0.01)	$ 0.04	$ (0.03)	$ (0.03)	$ 0.05	$ (0.14)	$ 0.04	$ 0.92
Net income (loss)	$ 1.04	$ 0.39	$ 0.58	$ 0.63	$ 0.66	$ 0.66	$ 0.54	$ (2.00)	$ 2.64	$ (0.06)	$ 2.47