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	$ 117,365	$ 107,857	$ 113,423	$ 108,936	$ 118,639	$ 111,510	$ 108,216	$ 103,606	$ 447,581	$ 441,971	$ 462,571
Domestic [Member] | U.S. [Member]
Schedule Of Net Sales By Geographical Segment [Line Items]
Net Sales									334,624	328,585	340,328
International [Member]
Schedule Of Net Sales By Geographical Segment [Line Items]
Net Sales									112,957	113,386	122,243
International [Member] | U.K. [Member]
Schedule Of Net Sales By Geographical Segment [Line Items]
Net Sales									8,431	8,206	12,509
International [Member] | Italy [Member]
Schedule Of Net Sales By Geographical Segment [Line Items]
Net Sales									18,742	17,447	19,181
International [Member] | Brazil [Member]
Schedule Of Net Sales By Geographical Segment [Line Items]
Net Sales									31,166	34,424	31,112
International [Member] | Others [Member]
Schedule Of Net Sales By Geographical Segment [Line Items]
Net Sales									$ 54,618	$ 53,309	$ 59,441