Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Estimated Useful Lives and Residual Values of Company's Rental Equipment

The estimated useful lives and residual values of the Company’s rental equipment used for financial reporting purposes are as follows:

Relocatable modular buildings	18 years, 50% residual value
Relocatable modular accessories	3 to 18 years, no residual value
Portable storage containers	25 years, 62.5% residual value
Electronic test equipment and accessories	1 to 8 years, no residual value
Liquid and solid containment tanks and boxes and accessories	3 to 20 years, no residual value

Property, Plant and Equipment

Property, plant and equipment consist of the following:

(dollar amounts in thousands)	Estimated useful life		December 31,
	in years		2017			2016
Land	Indefinite		$	50,689		$	45,928
Land improvements	20 – 50			43,337			42,677
Buildings		30		26,862			26,105
Furniture, office and computer equipment	3 – 10			32,118			35,215
Vehicles and machinery	5 – 25			34,597			30,416
				187,603			180,341
Less accumulated depreciation				(70,034	)		(68,854	)
				117,569			111,487
Construction in progress				1,601			703
			$	119,170		$	112,190

Weighted-Average Common Stock Used to Calculate Basic and Diluted Earnings per Share

The table below presents the weighted-average common stock used to calculate basic and diluted earnings per share:

(in thousands)	Year Ended December 31,
	2017		2016		2015
Weighted-average common stock for calculating basic    earnings per share		23,999		23,900		25,369
Effect of potentially dilutive securities from equity-based    compensation		270		76		88
Weighted-average common stock for calculating diluted    earnings per share		24,269		23,976		25,457

Securities Not Included in Computation of Diluted Earnings Per Share

The following securities were not included in the computation of diluted earnings per share as their effect would have been anti-dilutive:

(in thousands)	Year Ended December 31,
	2017		2016		2015
Options to purchase common stock		7		661		746

Summary of Allowance for Doubtful Accounts Activity

The allowance for doubtful accounts activity was as follows:

(in thousands)	2017			2016
Beginning balance, January 1	$	2,087		$	2,087
Provision for doubtful accounts		1,480			1,892
Write-offs, net of recoveries		(1,647	)		(1,892	)
Ending balance, December 31	$	1,920		$	2,087