Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
OPERATING ACTIVITIES
Net income	$ 14,079	$ 19,734
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	24,849	15,232
Deferred income taxes	3,716	3,178
Amortization of stock-based compensation	261	354
Gain on disposal of property and equipment	(2,043)	(11,178)
Changes in certain working capital items:
Trade receivables	(6,765)	(5,192)
Prepaid expenses and other current assets	(1,659)	(2,052)
Accounts payable, accrued liabilities, and accrued expenses	(2,802)	1,393
Accrued income taxes	2,353	6,985
Net cash provided by operating activities	31,989	28,454
INVESTING ACTIVITIES
Proceeds from sale of property and equipment	4,840	17,452
Purchases of property and equipment, net of trades	(21,560)	(38,232)
Maturity and calls of investments	0	25
Payments to Acquire Business, Net of Cash Acquired	(3,011)	0
Change in other assets	(90)	(31)
Net cash (used in) provided by investing activities	(19,821)	(20,786)
FINANCING ACTIVITIES
Repayment of long-term debt	(13,000)	0
Net cash used in financing activities	(13,000)	0
Net (decrease) increase in cash and cash equivalents	(832)	7,668
CASH AND CASH EQUIVALENTS
Beginning of period	17,763	119,838
End of period	16,931	127,506
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Interest Paid	163	0
Cash paid during the period for income taxes, net of refunds	421	434
Noncash investing and financing activities:
Fair value of revenue equipment traded	3,198	0
Purchased property and equipment in accounts payable	10,142	18,752
Common Stock Dividends Declared In Accounts Payable	$ 1,758	$ 1,701