Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Cash flows from operating activities:
Net income	$ 3,276	$ 4,262
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	4,694	4,643
Amortization of deferred loan costs	76	76
Stock-based compensation	263	236
Provision (recoveries) of bad debts	29	(34)
Loss on disposal of assets		(21)
Changes in operating assets and liabilities:
Receivables	219	251
Inventories	281	18
Prepaid expenses	(938)	(729)
Accounts payable	(1,303)	290
Accrued expenses	(517)	705
Income taxes	1,768	2,157
Net cash provided by operating activities	7,848	11,854
Cash flows from investing activities:
Proceeds from sale of assets		21
Change in construction payable	1,204
Acquisition of property and equipment	(4,960)	(2,396)
Net cash used in investing activities	(3,756)	(2,375)
Cash flows from financing activities:
Net exercise of stock options	(1,429)
Principal payments on long-term debt	(4,900)	(9,300)
Net cash used in financing activities	(6,329)	(9,300)
Net (decrease) increase in cash	(2,237)	179
Cash and cash equivalents at beginning of period	19,330	19,043
Cash and cash equivalents at end of period	17,093	19,222
Supplemental disclosure of cash flow information
Cash paid for interest , net of amounts capitalized	242	479
Cash paid for income taxes		$ 200