Restatement of previously issued consolidated financial statements Restatement of statements of operations (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009
Net sales [Member]
Restatement of certain financial statement line items	$ 282,357	$ 228,431
Sales [Member]
Restatement of certain financial statement line items	282,959	228,971
Gross profit [Member]
Restatement of certain financial statement line items	128,970	106,276
Income from operations [Member]
Restatement of certain financial statement line items	47,656	35,426
Income before income taxes [Member]
Restatement of certain financial statement line items	47,785	36,607
Provision for income taxes [Member]
Restatement of certain financial statement line items	(17,862)	(11,626)
Net Income [Member]
Restatement of certain financial statement line items	29,923	24,981
Earnings Per Share, Basic [Member]
Restatement of certain financial statement line items	0	0
Earnings Per Share, Diluted [Member]
Restatement of certain financial statement line items	0	0
Retained Earnings [Member]
Restatement of certain financial statement line items	256,208	226,285
Stockholders' Equity, Total [Member]
Restatement of certain financial statement line items	271,704	263,429
Comprehensive Income [Member]
Restatement of certain financial statement line items	27,672	25,266
Accounts receivable change [Member]
Restatement of certain financial statement line items	(6,378)	(6,501)
Prepaid and deferred income taxes, including excess tax benefits change [Member]
Restatement of certain financial statement line items	1,460	2,164
Net sales [Member]
Restatement of certain financial statement line items	(1,623)	(2,542)
Sales [Member]
Restatement of certain financial statement line items	(1,623)	(2,542)
Gross profit [Member]
Restatement of certain financial statement line items	(1,623)	(2,542)
Income from operations [Member]
Restatement of certain financial statement line items	(1,623)	(2,542)
Income before income taxes [Member]
Restatement of certain financial statement line items	(1,623)	(2,542)
Provision for income taxes [Member]
Restatement of certain financial statement line items	617	966
Net Income [Member]
Restatement of certain financial statement line items	(1,006)	(1,576)
Earnings Per Share, Basic [Member]
Restatement of certain financial statement line items	0	0
Earnings Per Share, Diluted [Member]
Restatement of certain financial statement line items	0	0
Retained Earnings [Member]
Restatement of certain financial statement line items	(2,582)	(1,576)
Stockholders' Equity, Total [Member]
Restatement of certain financial statement line items	(2,582)	(1,576)
Comprehensive Income [Member]
Restatement of certain financial statement line items	(1,006)	(1,576)
Accounts receivable change [Member]
Restatement of certain financial statement line items	1,623	2,542
Prepaid and deferred income taxes, including excess tax benefits change [Member]
Restatement of certain financial statement line items	(617)	(966)
Net sales [Member]
Restatement of certain financial statement line items	283,980	230,973
Sales [Member]
Restatement of certain financial statement line items	284,582	231,513
Gross profit [Member]
Restatement of certain financial statement line items	130,593	108,818
Income from operations [Member]
Restatement of certain financial statement line items	49,279	37,968
Income before income taxes [Member]
Restatement of certain financial statement line items	49,408	39,149
Provision for income taxes [Member]
Restatement of certain financial statement line items	(18,479)	(12,592)
Net Income [Member]
Restatement of certain financial statement line items	30,929	26,557
Earnings Per Share, Basic [Member]
Restatement of certain financial statement line items	0	0
Earnings Per Share, Diluted [Member]
Restatement of certain financial statement line items	0	0
Retained Earnings [Member]
Restatement of certain financial statement line items	258,790	227,861
Stockholders' Equity, Total [Member]
Restatement of certain financial statement line items	274,286	265,005
Comprehensive Income [Member]
Restatement of certain financial statement line items	28,678	26,842
Accounts receivable change [Member]
Restatement of certain financial statement line items	(8,001)	(9,043)
Prepaid and deferred income taxes, including excess tax benefits change [Member]
Restatement of certain financial statement line items	$ 2,077	$ 3,130