Business segment information - Summary of Net Sales by Geographic Destination (Detail) (USD $) In Thousands, 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
Schedule Of Net Sales By Geographical Segment [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
Domestic [Member] | U.S. [Member]
Schedule Of Net Sales By Geographical Segment [Line Items]
Net Sales									341,015	329,625	339,781
International [Member]
Schedule Of Net Sales By Geographical Segment [Line Items]
Net Sales									121,305	140,496	120,848
International [Member] | U.K. [Member]
Schedule Of Net Sales By Geographical Segment [Line Items]
Net Sales									8,628	8,240	12,509
International [Member] | Italy [Member]
Schedule Of Net Sales By Geographical Segment [Line Items]
Net Sales									18,242	20,700	19,831
International [Member] | Brazil [Member]
Schedule Of Net Sales By Geographical Segment [Line Items]
Net Sales									38,015	48,851	29,067
International [Member] | Others [Member]
Schedule Of Net Sales By Geographical Segment [Line Items]
Net Sales									$ 56,420	$ 62,705	$ 59,441