Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
OPERATING ACTIVITIES:
Net income	$ 8,676,000	$ 3,892,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	24,358,000	21,156,000
Bad debt expense	389,000	118,000
Stock compensation-net of excess tax benefits	395,000	284,000
Provision for deferred income taxes	2,158,000	2,325,000
Reclassification of unrealized loss on marketable equity securities		27,000
Recognized loss (gain) on marketable equity securities	810,000	(2,145,000)
(Gain)loss on sale or disposition of equipment	(515,000)	130,000
Changes in operating assets and liabilities:
Accounts receivable	(17,258,000)	(2,103,000)
Prepaid expenses, deposits, inventories, and other assets	3,314,000	3,083,000
Income taxes refundable	124,000	27,000
Trade accounts payable	5,361,000	(1,938,000)
Accrued expenses and other liabilities	1,712,000	1,403,000
Net cash provided by operating activities	29,524,000	26,259,000
INVESTING ACTIVITIES:
Purchases of property and equipment	(39,768,000)	(14,372,000)
Proceeds from disposition of equipment	4,450,000	5,507,000
Sales of marketable equity securities		3,079,000
Purchases of marketable equity securities, net of return of capital	(2,006,000)	13,000
Net cash used in investing activities	(37,324,000)	(5,773,000)
FINANCING ACTIVITIES:
Borrowings under line of credit	299,959,000	218,678,000
Repayments under line of credit	(274,702,000)	(220,543,000)
Borrowings of long-term debt	25,046,000	7,821,000
Repayments of long-term debt	(37,002,000)	(21,786,000)
Borrowings under margin account	2,166,000	81,000
Repayments under margin account	(565,000)	(3,604,000)
Repurchases of common stock	(7,531,000)	(1,193,000)
Exercise of stock options	468,000	112,000
Net cash provided by (used in) financing activities	7,839,000	(20,434,000)
NET INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	39,000	52,000
CASH, CASH EQUIVALENTS AND RESTRICTED CASH -Beginning of period	224,000	137,000
CASH, CASH EQUIVALENTS AND RESTRICTED CASH -End of period	263,000	189,000
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION-
Interest	2,452,000	1,931,000
Income taxes	53,000	106,000
NONCASH INVESTING AND FINANCING ACTIVITIES-
Purchases of property and equipment included in accounts payable	$ 9,888,000	$ 2,939,000