Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Operating activities:
Net income	$ 212,864		$ 173,860
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of property, equipment and intangibles	54,950		47,477
Amortization of debt discount and issuance costs	525		520
Excess tax benefit from stock options exercised	(21,188)		(17,850)
Deferred income taxes	(4,441)		(3,796)
Share-based compensation programs	5,890		5,096
Other	1,355		1,526
Changes in operating assets and liabilities:
Accounts receivable	(19,867)		(13,016)
Inventory	26,807		(21,994)
Accounts payable	53,582		104,376
Income taxes payable	117,221		69,922
Other	(21,673)		(572)
Net cash provided by operating activities	406,025		345,549
Investing activities:
Purchases of property and equipment	(91,140)		(83,085)
Proceeds from sale of property and equipment	658		287
Payments received on notes receivable	935		900
Net cash used in investing activities	(89,547)		(81,898)
Financing activities:
Principal payments on capital leases	(19)		(18)
Repurchases of common stock	(134,813)		(22,067)
Excess tax benefit from stock options exercised	21,188		17,850
Net proceeds from issuance of common stock	20,252		21,097
Net cash (used in) provided by financing activities	(93,392)		16,862
Net increase in cash and cash equivalents	223,086		280,513
Cash and cash equivalents at beginning of the period	250,560	[1]	231,318
Cash and cash equivalents at end of the period	473,646		511,831
Supplemental disclosures of cash flow information:
Income taxes paid	8,675		33,331
Interest paid, net of capitalized interest	$ 23,435		$ 22,419

[1] The balance sheet at December 31, 2014, has been derived from the audited consolidated financial statements at that date, but does not include all of the information and footnotes required by United States generally accepted accounting principles for complete financial statements.