CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 34,098	$ 25,538	$ 24,574
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14,617	15,132	14,835
Amortization of deferred loan costs	538	538	410
Stock-based compensation	5,468	7,091	1,681
Excess tax benefit from stock-based compensation			(737)
Provision for bad debts	93	103	74
Loss on disposition of assets	12	4	677
Deferred income taxes	(483)	3,810	798
Changes in operating assets and liabilities:
Receivables	92	(1,992)	(1,381)
Income taxes	1,729	(1,600)	203
Inventories	(357)	(238)	(216)
Prepaid expenses	(896)	(125)	(1,085)
Accounts payable	2,998	(431)	1,973
Accrued expenses	847	1,624	1,922
Net cash provided by operating activities	58,756	49,454	43,728
Cash flows from investing activities:
Proceeds from sale of assets		86	29
Change in construction payable	11,329	3,218	1,198
Acquisition of property and equipment	(137,074)	(49,990)	(26,121)
Net cash used in investing activities	(125,745)	(46,686)	(24,894)
Cash flows from financing activities:
Net exercise of stock options			2,934
Excess tax benefit from stock-based compensation			737
Loan issuance cost			(2,586)
Long-term debt borrowings (principal payment)	68,300		(14,700)
Net cash provided by (used in) financing activities	68,300		(13,615)
Change in cash	1,311	2,768	5,219
Cash and cash equivalents at beginning of period	29,151	26,383	21,164
Cash and cash equivalents at end of period	30,462	29,151	26,383
Supplemental disclosure of cash flow information:
Cash paid for interest, net of amounts capitalized	186	426	206
Cash paid for income taxes	7,305	11,950	$ 12,375
Return of assets under capital lease:
Accounts payable		(105)
Accrued expenses		$ (13)
ASC 606 Changes | ASU 2014-09
Adjustment to beginning retained earnings for accounting changes in accordance with the new revenue recognition standard
Accrued expenses	$ (4,858)