Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating Activities
Net income	$ 132,331	$ 109,241
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	12,450	10,477
Stock-based compensation	5,919	5,844
(Gain) loss on disposal of property, plant and equipment	(138)	90
Other non-cash adjustments	(28)	(372)
Changes in operating assets and liabilities:
Accounts receivable	(174,954)	(26,225)
Inventories	4,525	13,878
Prepaid expenses and other assets	(694)	2,129
Accounts payable	14,447	(6,443)
Accrued expenses and other liabilities	13,286	(10,262)
Income taxes receivable/payable	5,370	629
Net cash provided by operating activities	12,514	98,986
Investing Activities
Expenditures for property, plant and equipment	(99,696)	(36,926)
Proceeds from sales of property, plant and equipment	2,150	21
Net cash used in investing activities	(97,546)	(36,905)
Financing Activities
Borrowings under line of credit	235,000	89,500
Principal payments under line of credit	(235,000)	(89,500)
Repurchases of common stock	(44,437)	(35,216)
Proceeds from employee stock purchase and option plans	1,078	718
Financing costs	(361)
Net cash used in financing activities	(43,720)	(34,498)
Net (decrease) increase in cash and cash equivalents	(128,752)	27,583
Cash and cash equivalents, beginning of period	148,833	105,699
Cash and cash equivalents, end of period	20,081	133,282
Supplemental Disclosure:
Cash paid for interest	155	321
Cash paid for income taxes, net	$ 38,567	$ 32,872