CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 25,538	$ 24,574	$ 20,659
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	15,132	14,835	15,933
Amortization of deferred loan costs	538	410	338
Stock-based compensation	7,091	1,681	1,544
Excess tax benefit from stock-based compensation		(737)	(865)
Provision for bad debts	103	74	240
Loss on disposition of assets	4	677	(9)
Deferred income taxes	3,810	798	(241)
Changes in operating assets and liabilities:
Receivables	(1,992)	(1,381)	(922)
Income taxes receivable	(1,600)	203	528
Inventories	(238)	(216)	(35)
Prepaid expenses	(125)	(1,085)	(289)
Accounts payable	(431)	1,973	(1,186)
Accrued expenses	1,624	1,922	2,546
Net cash provided by operating activities	49,454	43,728	38,241
Cash flows from investing activities:
Proceeds from sale of assets	86	29	34
Change in construction payable	3,218	1,198	(383)
Acquisition of property and equipment	(49,990)	(26,121)	(37,676)
Net cash used in investing activities	(46,686)	(24,894)	(38,025)
Cash flows from financing activities:
Net exercise of stock options		2,934	3,900
Excess tax benefit from stock-based compensation		737	865
Loan issuance cost		(2,586)
Principal payments on long-term debt		(14,700)	(5,400)
Net cash used in financing activities		(13,615)	(635)
Net increase (decrease) in cash	2,768	5,219	(419)
Cash and cash equivalents at beginning of period	26,383	21,164	21,583
Cash and cash equivalents at end of period	29,151	26,383	21,164
Supplemental disclosure of cash flow information
Cash paid for interest, net of amounts capitalized	426	206	374
Cash paid for income taxes	11,950	$ 12,375	$ 10,930
Return of assets under capital lease:
Accounts Payable	(105)
Accrued Expenses	$ (13)