Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
OPERATING ACTIVITIES:
Net income	$ 1,387,000	$ 2,283,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	11,623,000	10,671,000
Bad debt expense	158,000	36,000
Stock compensation-net of excess tax benefits	233,000	115,000
Provision for deferred income taxes	295,000	1,387,000
Recognized loss (gain) on marketable equity securities	1,142,000	(1,782,000)
Loss (gain) on sale or disposition of equipment	3,000	(1,000)
Changes in operating assets and liabilities:
Accounts receivable	(6,693,000)	(3,918,000)
Prepaid expenses, deposits, inventories, and other assets	1,633,000	1,321,000
Income taxes refundable	31,000	51,000
Trade accounts payable	4,414,000	197,000
Accrued expenses and other liabilities	1,494,000	1,999,000
Net cash provided by operating activities	15,720,000	12,359,000
INVESTING ACTIVITIES:
Purchases of property and equipment	(13,220,000)	(4,038,000)
Proceeds from disposition of equipment	756,000	4,005,000
Sales of marketable equity securities		2,368,000
Purchases of marketable equity securities, net of return of capital	(582,000)	28,000
Net cash used in investing activities	(13,046,000)	2,363,000
FINANCING ACTIVITIES:
Borrowings under line of credit	130,935,000	104,149,000
Repayments under line of credit	(126,372,000)	(105,511,000)
Borrowings of long-term debt	6,949,000
Repayments of long-term debt	(14,674,000)	(10,795,000)
Borrowings under margin account	669,000	41,000
Repayments under margin account	(290,000)	(2,631,000)
Repurchases of common stock	(36,000)
Exercise of stock options	168,000	46,000
Net cash used in financing activities	(2,651,000)	(14,701,000)
NET INCREASE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	23,000	21,000
CASH, CASH EQUIVALENTS AND RESTRICTED CASH -Beginning of period	224,000	137,000
CASH, CASH EQUIVALENTS AND RESTRICTED CASH -End of period	247,000	158,000
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION-
Interest	1,164,000	989,000
Income taxes	5,000	16,000
NONCASH INVESTING AND FINANCING ACTIVITIES-
Purchases of property and equipment included in accounts payable	$ 2,431,000	$ 29,000