Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:
Net income	$ 64,610	$ 77,053
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	127,310	124,078
Deferred income taxes	(8,418)	(7,920)
Gain on disposal of property and equipment	(12,701)	(15,798)
Stock-based compensation	3,829	3,374
Insurance and claims accruals, net of current portion	2,700	(50)
Other	(1,239)	1,366
Changes in certain working capital items:
Accounts receivable, net	(25,725)	954
Other current assets	568	21,355
Accounts payable	13,899	(10,235)
Other current liabilities	6,258	4,538
Net cash provided by operating activities	171,091	198,715
Cash flows from investing activities:
Additions to property and equipment	(149,889)	(226,499)
Retirements of property and equipment	43,421	46,252
Decrease in notes receivable	7,095	4,114
Other	979	0
Net cash used in investing activities	(98,394)	(176,133)
Cash flows from financing activities:
Repayments of short-term debt	(20,000)	(140,000)
Proceeds from issuance of short-term debt	0	140,000
Repayments of long-term debt	(30,000)	0
Proceeds from issuance of long-term debt	10,000	0
Change in net checks issued in excess of cash balances	0	(6,671)
Dividends on common stock	(10,961)	(10,929)
Repurchases of common stock	(20,060)	0
Tax withholding related to net share settlements of restricted stock awards	(560)	(146)
Stock options exercised	969	379
Excess tax benefits from exercise of stock options	53	22
Net cash used in financing activities	(70,559)	(17,345)
Effect of exchange rate fluctuations on cash	(216)	388
Net increase in cash and cash equivalents	1,922	5,625
Cash and cash equivalents, beginning of period	15,428	12,412
Cash and cash equivalents, end of period	17,350	18,037
Supplemental disclosures of cash flow information:
Interest paid	361	225
Income taxes paid	54,423	49,324
Supplemental schedule of non-cash investing activities:
Notes receivable issued upon sale of property and equipment	12,701	7,286
Property and equipment acquired included in accounts payable	2,696	7,991
Property and equipment disposed included in other receivables	$ 696	$ 411