Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ 1,034,375,000	$ 672,682,000	$ 615,518,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	259,899,000	261,267,000	253,681,000
Noncash lease expense	14,890,000	11,963,000	11,066,000
(Gain) loss on disposal of property and equipment	(563,000)	736,000	6,066,000
Deferred income taxes	30,165,000	(41,011,000)	13,157,000
Share-based compensation	15,039,000	11,337,000	16,717,000
Changes in assets and liabilities:
Customer and other receivables, net	(125,562,000)	(49,045,000)	30,330,000
Prepaid expenses and other assets	(38,387,000)	(1,722,000)	(16,807,000)
Accounts payable	14,008,000	(1,743,000)	(8,264,000)
Compensation, benefits and other accrued liabilities	32,437,000	72,928,000	3,263,000
Claims and insurance accruals	10,963,000	(1,459,000)	5,297,000
Income taxes, net	(27,929,000)	8,750,000	32,612,000
Other liabilities	(6,729,000)	(11,659,000)	21,252,000
Net cash provided by operating activities	1,212,606,000	933,024,000	983,888,000
Cash flows from investing activities:
Purchase of property and equipment	(550,077,000)	(225,081,000)	(479,325,000)
Proceeds from sale of property and equipment	19,548,000	3,690,000	5,686,000
Purchase of short-term investments	(359,389,000)	(360,160,000)
Proceeds from maturities of short-term investments	435,130,000	29,988,000
Other investing activities, net	(500,000)	(100,000)
Net cash used in investing activities	(455,288,000)	(551,663,000)	(473,639,000)
Cash flows from financing activities:
Proceeds from issuance of long-term debt		99,923,000
Principal payments under debt agreements		(45,000,000)
Dividends paid	(92,366,000)	(71,023,000)	(54,552,000)
Payments for share repurchases	(536,465,000)	(364,057,000)	(240,960,000)
Forward contract for accelerated share repurchases	(62,500,000)
Other financing activities, net	(4,853,000)	(3,345,000)	(1,448,000)
Net cash used in financing activities	(696,184,000)	(383,502,000)	(296,960,000)
Increase (decrease) in cash and cash equivalents	61,134,000	(2,141,000)	213,289,000
Cash and cash equivalents at beginning of year	401,430,000	403,571,000	190,282,000
Cash and cash equivalents at end of year	462,564,000	401,430,000	403,571,000
Income taxes paid	352,826,000	266,506,000	157,290,000
Interest paid	4,232,000	5,686,000	3,857,000
Capitalized interest	2,655,000	$ 2,473,000	$ 3,128,000
Supplemental disclosure of noncash investing and financing activities:
Noncash purchases of property	$ 16,034,000