Condensed Income Statements (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Revenue:
Rental income	$ 20,603	$ 18,789
Sales, net	3,912us-gaap_SalesRevenueGoodsNet	3,338us-gaap_SalesRevenueGoodsNet
Service and maintenance income	226us-gaap_SalesRevenueServicesNet	195us-gaap_SalesRevenueServicesNet
Total revenue	24,741us-gaap_SalesRevenueNet	22,322us-gaap_SalesRevenueNet
Operating costs and expenses:
Cost of rentals, exclusive of depreciation stated separately below	7,727	7,956
Cost of sales, exclusive of depreciation stated separately below	2,813us-gaap_OtherCostOfOperatingRevenue	2,235us-gaap_OtherCostOfOperatingRevenue
Cost of service and maintenance, exclusive of depreciation and amortization stated separately below	38us-gaap_OtherCostOfServices	84us-gaap_OtherCostOfServices
Selling, general, and administrative expense	2,588	2,643
Depreciation and amortization	5,788	5,042
Total operating costs and expenses	18,954us-gaap_CostsAndExpenses	17,960us-gaap_CostsAndExpenses
Operating income	5,787us-gaap_OperatingIncomeLoss	4,362us-gaap_OperatingIncomeLoss
Other income (expense):
Interest expense	(3)us-gaap_InterestExpense	(2)us-gaap_InterestExpense
Other income	42us-gaap_OtherNonoperatingIncomeExpense	5us-gaap_OtherNonoperatingIncomeExpense
Total other income (expense)	39us-gaap_NonoperatingIncomeExpense	3us-gaap_NonoperatingIncomeExpense
Income before provision for income taxes	5,826	4,365
Provision for income taxes	2,132us-gaap_IncomeTaxExpenseBenefit	1,509us-gaap_IncomeTaxExpenseBenefit
Net income	$ 3,694us-gaap_NetIncomeLoss	$ 2,856us-gaap_NetIncomeLoss
Earnings per share:
Basic (in USD per share)	$ 0.30us-gaap_EarningsPerShareBasic	$ 0.23us-gaap_EarningsPerShareBasic
Diluted (in USD per share)	$ 0.29us-gaap_EarningsPerShareDiluted	$ 0.23us-gaap_EarningsPerShareDiluted
Weighted average shares outstanding:
Basic (in shares)	12,504	12,373
Diluted (in shares)	12,713	12,692

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