Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating Activities
Net income	$ 42,402	$ 31,555
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation and amortization	3,851	3,394
Stock-based compensation	2,775	2,793
(Gain) loss on disposal of property, plant and equipment	(123)	10
Other non-cash adjustments	32	31
Changes in operating assets and liabilities:
Accounts receivable	(162,780)	(128,182)
Inventories	(2,610)	7,645
Prepaid expenses and other assets	1,059	1,214
Accounts payable	8,865	(7,556)
Accrued expenses and other liabilities	(14,089)	(27,332)
Income taxes receivable/payable	11,850	6,438
Net cash used in operating activities	(108,768)	(109,990)
Investing Activities
Expenditures for property, plant and equipment	(22,733)	(8,647)
Proceeds from sales of property, plant and equipment	2,136
Net cash used in investing activities	(20,597)	(8,647)
Financing Activities
Borrowings under line of credit	36,500	35,000
Principal payments under line of credit	(8,000)
Repurchases of common stock	(42,929)	(14,457)
Proceeds from employee stock purchase and option plans	300	302
Net cash (used in) provided by financing activities	(14,129)	20,845
Net decrease in cash and cash equivalents	(143,494)	(97,792)
Cash and cash equivalents, beginning of period	148,833	105,699
Cash and cash equivalents, end of period	5,339	7,907
Supplemental Disclosure:
Cash paid for interest	1	11
Cash paid for income taxes, net	$ 1,405	$ 1,262