CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 24,574	$ 20,659	$ 14,185
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14,835	15,933	17,824
Amortization of deferred loan costs	410	338	305
Stock-based compensation	1,681	1,544	1,226
Excess tax benefit from stock-based compensation	(737)	(865)	(1,079)
Provision for bad debts	74	240	51
Loss (gain) on disposition of assets	677	(9)	343
Deferred income taxes	798	(241)	336
Changes in operating assets and liabilities:
Receivables	(1,381)	(922)	(470)
Inventories	(216)	(35)	(171)
Prepaid expenses	(1,085)	(289)	(1,191)
Accounts payable	1,973	(1,186)	(733)
Accrued expenses	1,922	2,546	1,150
Income taxes	203	528	(531)
Net cash provided by operating activities	43,728	38,241	31,245
Cash flows from investing activities:
Proceeds from sale of assets	29	34	84
Change in construction payable	1,198	(383)	1,790
Acquisition of property and equipment	(26,121)	(37,676)	(21,719)
Net cash used in investing activities	(24,894)	(38,025)	(19,845)
Cash flows from financing activities:
Net exercise of stock options	2,934	3,900	(2,726)
Excess tax benefit from stock-based compensation	737	865	1,079
Principal payments on long-term debt	(14,700)	(5,400)	(7,500)
Loan issuance cost	(2,586)
Net cash used in financing activities	(13,615)	(635)	(9,147)
Net increase (decrease) in cash	5,219	(419)	2,253
Cash and cash equivalents at beginning of period	21,164	21,583	19,330
Cash and cash equivalents at end of period	26,383	21,164	21,583
Supplemental disclosure of cash flow information
Cash paid for interest, net of amounts capitalized	206	374	853
Cash paid for income taxes	$ 12,375	10,930	$ 7,300
Conversion of short term deposit to long term deposit		$ 908