Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating Activities:
Net income	$ 37,291	$ 28,111
Noncash items included in net income:
Depreciation and amortization	35,372	32,590
Deferred income taxes	1,327	7,069
Other, net	2,365	2,129
Changes in operating assets and liabilities, net	(15,384)	(18,632)
Net cash provided by operating activities	60,971	51,267
Investing Activities:
Acquisition of property and equipment	(25,568)	(107,591)
Proceeds from disposal of property and equipment	180	4,915
Net cash used in investing activities	(25,388)	(102,676)
Financing Activities:
Repayment of revolving credit agreement	(7,713)	(86,734)
Borrowing of revolving credit agreement	7,713	190,874
Proceeds from stock option exercises	3,678	2,137
Shares withheld for taxes	(6,350)	(3,404)
Repayment of finance leases	(4,959)	(4,803)
Net cash provided by (used in) financing activities	(7,631)	98,070
Net Increase in Cash and Cash Equivalents	27,952	46,661
Cash and cash equivalents, beginning of period	25,308	248
Cash and cash equivalents, end of period	$ 53,260	$ 46,909