Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Activities
Net income	$ 134,572	$ 95,128	$ 67,847
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	16,597	16,860	14,498
Deferred income taxes	1,037	194	5,433
Stock-based compensation	6,344	5,187	4,788
Loss (Gain) on disposal of property, plant and equipment	47	1,738	(185)
Other non-cash adjustments	(406)	(406)	(284)
Changes in operating assets and liabilities:
Accounts receivable	(24,281)	(10,486)	(653)
Inventories	(23,276)	(3,635)	(5,442)
Prepaid expenses and other assets	(613)	(2,194)	(4,256)
Accounts payable	21,131	(4,804)	(6,966)
Accrued expenses and other liabilities	5,040	2,488	9,403
Income taxes receivable/payable	1,929	1,795	1,110
Net cash provided by operating activities	138,121	101,865	85,293
Investing Activities
Expenditures for property, plant and equipment and intangibles	(33,816)	(15,040)	(14,551)
Proceeds from sales of property, plant and equipment	83	55	4,349
Acquisition of business, net of cash acquired		(71,804)
Net cash used in investing activities	(33,733)	(86,789)	(10,202)
Financing Activities
Financing costs			(485)
Borrowings under line of credit	172,250	201,000	242,700
Principal payments under line of credit	(172,250)	(201,000)	(249,700)
Repurchases of common stock	(30,085)	(3,617)	(55,216)
Proceeds from employee stock purchase and option plans	882	391	279
Net cash used in financing activities	(29,203)	(3,226)	(62,422)
Net increase in cash and cash equivalents	75,185	11,850	12,669
Cash and cash equivalents at beginning of year	30,514	18,664	5,995
Cash and cash equivalents at end of year	105,699	30,514	18,664
Supplemental disclosures of cash flow information:
Cash paid for interest	662	418	852
Cash paid for income taxes, net	$ 48,238	$ 44,802	$ 28,626