Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Operating Activities
Net income	$ 109,910	$ 89,620
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation and amortization	15,702	7,915
Stock-based compensation	4,308	4,303
Gain on disposal of property, plant and equipment	(1,083)	(134)
Other non-cash adjustments	(226)	(233)
Changes in operating assets and liabilities:
Accounts receivable	(157,117)	(171,220)
Inventories	(8,994)	6,457
Prepaid expenses and other assets	(6,878)	(2,335)
Accounts payable	14,907	12,195
Accrued expenses and other liabilities	10,763	(591)
Income taxes receivable/payable	466	21,691
Net cash used in operating activities	(18,242)	(32,332)
Investing Activities
Expenditures for property, plant and equipment	(94,831)	(62,613)
Proceeds from sales of property, plant and equipment	1,314	2,146
Net cash used in investing activities	(93,517)	(60,467)
Financing Activities
Borrowings under line of credit	286,000	173,000
Principal payments under line of credit	(236,500)	(173,000)
Repurchases of common stock	(54,832)	(44,124)
Financing costs		(361)
Proceeds from employee stock purchase and option plans	860	688
Net cash used in financing activities	(4,472)	(43,797)
Net decrease in cash and cash equivalents	(116,231)	(136,596)
Cash and cash equivalents, beginning of period	121,701	148,833
Cash and cash equivalents, end of period	5,470	12,237
Supplemental Disclosure:
Cash paid for interest, net of amounts capitalized		143
Cash paid for income taxes, net	$ 36,457	$ 7,813