Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating Activities
Net income	$ 48,545	$ 42,402
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation and amortization	6,423	3,851
Stock-based compensation	2,176	2,775
Gain on disposal of property, plant and equipment	(98)	(123)
Other non-cash adjustments	77	32
Changes in operating assets and liabilities:
Accounts receivable	(202,781)	(162,780)
Inventories	(6,774)	(2,610)
Prepaid expenses and other assets	(809)	1,059
Accounts payable	10,494	8,865
Accrued expenses and other liabilities	(14,453)	(14,089)
Income taxes receivable/payable	14,626	11,850
Net cash used in operating activities	(142,574)	(108,768)
Investing Activities
Expenditures for property, plant and equipment	(58,093)	(22,733)
Proceeds from sales of property, plant and equipment	293	2,136
Net cash used in investing activities	(57,800)	(20,597)
Financing Activities
Borrowings under line of credit	142,000	36,500
Principal payments under line of credit	(6,000)	(8,000)
Repurchases of common stock	(49,566)	(42,929)
Proceeds from employee stock purchase and option plans	460	300
Net cash provided by (used in) financing activities	86,894	(14,129)
Net decrease in cash and cash equivalents	(113,480)	(143,494)
Cash and cash equivalents, beginning of period	121,701	148,833
Cash and cash equivalents, end of period	8,221	5,339
Supplemental Disclosure:
Cash paid for interest	92	1
Cash paid for income taxes, net	$ 1,319	$ 1,405