Restatement and Revision of Prior Period Quarterly Financial Statements - Restated and Revised Consolidated Statements of Income Amounts (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenue	$ 305,367	$ 288,523	$ 280,066	$ 264,405	$ 275,727	$ 276,002	$ 272,212	$ 270,461	$ 544,471	$ 542,673	$ 832,994	$ 818,675	$ 1,138,361	$ 1,094,402	$ 1,028,892
Cost of Goods Sold		216,602	210,020	199,701		209,421	206,232	208,935	409,721	415,167	626,323	624,588	862,903	831,838	788,862
Gross profit	68,787	71,921	70,046	64,704	68,477	66,581	65,980	61,526	134,750	127,506	206,671	194,087	275,458	262,564	240,030
Selling, general and administrative		57,186	55,054	53,615		52,466	51,622	51,477	108,669	103,099	165,855	155,565	227,253	209,524	197,247
Income (loss) from operations		11,585	9,926	9,225		7,796	1,739	198	19,151	1,937	30,736	9,732	34,138	19,022	(13,213)
Income (loss) before taxes		10,844	7,736	8,032		6,517	1,069	(1,026)	15,768	42	26,612	6,559	27,718	14,783	(20,891)
Income tax expense (benefit)		3,728	3,362	2,354		2,292	2,974	2,110	5,716	5,084	9,444	7,376	11,288	10,834	11,498
Net income (loss)	$ (738)	$ 7,116	$ 4,374	$ 5,678	$ 4,765	$ 4,225	$ (1,905)	$ (3,136)	$ 10,052	$ (5,043)	$ 17,168	$ (817)	$ 16,430	$ 3,949	$ (32,389)
Basic earnings (loss) per share (in USD per share)	$ (0.01)	$ 0.13	$ 0.08	$ 0.11	$ 0.09	$ 0.08	$ (0.04)	$ (0.06)	$ 0.19	$ (0.09)	$ 0.32	$ (0.02)	$ 0.31	$ 0.07	$ (0.61)
Diluted earnings (loss) per share (in USD per share)	$ (0.01)	$ 0.13	$ 0.08	$ 0.10	$ 0.09	$ 0.08	$ (0.04)	$ (0.06)	$ 0.18	$ (0.09)	$ 0.31	$ (0.02)	$ 0.30	$ 0.07	$ (0.61)
Comprehensive income (loss)		$ 9,284	$ 8,253	$ 7,657		$ 4,024	$ (3,295)	$ (3,411)	$ 15,911	$ (6,708)	$ 25,196	$ (2,683)	$ 18,150	$ (3,198)	$ (40,640)
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenue	$ 300,950	288,386	279,530	267,390	$ 270,418	279,993	269,220	271,073	546,920	540,292	835,306	820,286	1,136,256	1,090,704	1,029,353
Cost of Goods Sold		215,867	209,303	203,113		212,212	204,126	209,127	412,416	413,253	628,282	625,465	857,921	827,156	789,159
Gross profit	71,311	72,519	70,227	64,277	68,727	67,781	65,093	61,946	134,504	127,039	207,024	194,821	278,335	263,548	240,194
Selling, general and administrative		57,134	55,086	53,427		52,601	51,418	51,492	108,513	102,910	165,647	155,511	225,738	209,967	197,291
Income (loss) from operations		12,236	10,075	8,986		8,860	1,056	603	19,061	1,659	31,297	10,520	38,530	19,563	(13,093)
Income (loss) before taxes		11,495	7,884	7,793		7,581	386	(621)	15,678	(235)	27,173	7,347	32,110	15,325	(20,771)
Income tax expense (benefit)		3,967	3,391	2,337		3,240	2,710	2,072	5,727	4,782	9,694	8,023	13,131	10,955	12,292
Net income (loss)	$ 1,500	$ 7,528	$ 4,493	$ 5,456	$ 5,047	$ 4,341	$ (2,324)	$ (2,693)	$ 9,951	$ (5,017)	$ 17,479	$ (676)	$ 18,979	$ 4,370	$ (33,063)
Basic earnings (loss) per share (in USD per share)	$ 0.03	$ 0.14	$ 0.08	$ 0.10	$ 0.09	$ 0.08	$ (0.04)	$ (0.05)	$ 0.19	$ (0.09)	$ 0.32	$ (0.01)	$ 0.35	$ 0.08	$ (0.63)
Diluted earnings (loss) per share (in USD per share)	$ 0.03	$ 0.14	$ 0.08	$ 0.10	$ 0.09	$ 0.08	$ (0.04)	$ (0.05)	$ 0.18	$ (0.09)	$ 0.32	$ (0.01)	$ 0.35	$ 0.08	$ (0.63)
Comprehensive income (loss)		$ 9,696	$ 8,373	$ 7,435		$ 4,140	$ (3,714)	$ (3,163)	$ 15,810	$ (6,877)	$ 25,506	$ (2,201)	$ 20,697	$ (2,436)	$ (41,655)
Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenue	$ 4,417	137	536	(2,985)	$ 5,309	(3,991)	2,992	(612)	(2,449)	2,381	(2,312)	(1,611)	2,105	3,698	(461)
Cost of Goods Sold		735	717	(3,412)		(2,791)	2,106	(192)	(2,695)	1,914	(1,959)	(877)	4,982	4,682	(297)
Gross profit	(2,524)	(598)	(181)	427	(250)	(1,200)	886	(420)	246	467	(353)	(734)	(2,877)	(984)	(164)
Selling, general and administrative		52	(32)	188		(135)	203	(15)	156	189	208	54	1,515	(443)	(44)
Income (loss) from operations		(649)	(149)	239		(1,064)	683	(405)	90	278	(561)	(788)	(4,392)	(541)	(120)
Income (loss) before taxes		(650)	(149)	239		(1,064)	683	(405)	90	277	(562)	(788)	(4,392)	(542)	(120)
Income tax expense (benefit)		(239)	(29)	17		(948)	264	38	(11)	302	(250)	(647)	(1,843)	(121)	(794)
Net income (loss)	$ (2,238)	$ (411)	$ (120)	$ 222	$ (282)	$ (116)	$ 419	$ (443)	$ 101	$ (26)	$ (311)	$ (141)	$ (2,549)	$ (421)	$ 674
Basic earnings (loss) per share (in USD per share)	$ (0.04)	$ (0.01)	$ 0.00	$ 0.01	$ 0.00	$ 0.00	$ 0.00	$ (0.01)	$ 0.00	$ 0.00	$ 0.00	$ (0.01)	$ (0.04)	$ (0.01)	$ 0.02
Diluted earnings (loss) per share (in USD per share)	$ (0.04)	$ (0.01)	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ (0.01)	$ 0.00	$ 0.00	$ (0.01)	$ (0.01)	$ (0.05)	$ (0.01)	$ 0.02
Comprehensive income (loss)		$ (411)	$ (120)	$ 222		$ (116)	$ 419	$ (248)	$ 101	$ 169	$ (311)	$ (482)	$ (2,547)	$ (762)	$ 1,015