Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating Activities
Net income	$ 183,705	$ 132,331
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	25,604	12,450
Stock-based compensation	6,195	5,919
Gain on disposal of property, plant and equipment	(1,057)	(138)
Other non-cash adjustments	(40)	(28)
Changes in operating assets and liabilities:
Accounts receivable	(158,813)	(174,954)
Inventories	(5,399)	4,525
Prepaid expenses and other assets	(4,311)	(694)
Accounts payable	17,219	14,447
Accrued expenses and other liabilities	28,472	13,286
Income taxes receivable/payable	21,484	5,370
Net cash provided by operating activities	113,059	12,514
Investing Activities
Expenditures for property, plant and equipment	(124,451)	(99,696)
Proceeds from sales of property, plant and equipment	1,355	2,150
Net cash used in investing activities	(123,096)	(97,546)
Financing Activities
Borrowings under line of credit	416,000	235,000
Principal payments under line of credit	(416,000)	(235,000)
Repurchases of common stock	(58,945)	(44,437)
Financing costs		(361)
Proceeds from employee stock purchase and option plans	1,323	1,078
Net cash used in financing activities	(57,622)	(43,720)
Net decrease in cash and cash equivalents	(67,659)	(128,752)
Cash and cash equivalents, beginning of period	121,701	148,833
Cash and cash equivalents, end of period	54,042	20,081
Supplemental Disclosure:
Cash paid for interest, net of amounts capitalized		155
Cash paid for income taxes, net	$ 39,750	$ 38,567