The Company’s four reportable segments are (1) its modular building and portable storage segment (“Mobile Modular”); (2) its electronic test equipment segment (“TRS-RenTelco”); (3) its containment solutions for the storage of hazardous and non-hazardous liquids and solids segment (“Adler Tanks”); and (4) its classroom manufacturing segment selling modular buildings used primarily as classrooms in California (“Enviroplex”). The operations of each of these segments are described in Part I – Item 1, “Business,” and the accounting policies of the segments are described in “Note 2 – Significant Accounting Policies” in the Company’s 2018 Annual Report. Management focuses on several key measures to evaluate and assess each segment’s performance, including rental revenue growth, gross profit, income from operations and income before provision for income taxes. Excluding interest expense, allocations of revenue and expense not directly associated with one of these segments are generally allocated to Mobile Modular, TRS-RenTelco and Adler Tanks based on their pro-rata share of direct revenues. Interest expense is allocated among Mobile Modular, TRS-RenTelco and Adler Tanks based on their pro-rata share of average rental equipment at cost, intangible assets, accounts receivable, deferred income and customer security deposits. The Company does not report total assets by business segment. Summarized financial information for the three months ended March 31, 2019 and 2018 for the Company’s reportable segments is shown in the following table:

(dollar amounts in thousands)	Mobile Modular			TRS- RenTelco			Adler Tanks			Enviroplex ¹			Consolidated
Three Months Ended March 31,
2019
Rental revenues	$	42,261		$	23,623		$	16,812		$ —			$	82,696
Rental related services revenues		14,471			708			6,276			—			21,455
Sales and other revenues		8,360			6,345			347			2,805			17,857
Total revenues		65,092			30,676			23,435			2,805			122,008
Depreciation of rental equipment		5,408			9,520			4,033			—			18,961
Gross profit		30,879			13,667			11,423			1,036			57,005
Selling and administrative expenses		15,370			5,970			7,080			1,275			29,695
Income (loss) from operations		15,509			7,697			4,343			(239	)		27,310
Interest (expense) income allocation		(1,883	)		(678	)		(827	)		280			(3,108	)
Income (loss) before provision for income taxes		13,626			7,068			3,516			41			24,251
Rental equipment acquisitions		20,938			12,808			1,694			—			35,440
Accounts receivable, net (period end)		71,816			20,925			19,151			7,511			119,403
Rental equipment, at cost (period end)		834,883			286,469			314,899		—				1,436,251
Rental equipment, net book value (period end)		585,248			132,607			195,023		—				912,878
Utilization (period end) ²		78.9	%		66.5	%		59.2	%
Average utilization ²		78.8	%		64.3	%		57.3	%
2018
Rental revenues	$	37,027		$	21,529		$	15,705		$ —			$	74,261
Rental related services revenues		11,934			807			5,090			—			17,831
Sales and other revenues		4,890			5,702			383			2,018			12,993
Total revenues		53,851			28,038			21,178			2,018			105,085
Depreciation of rental equipment		5,248			8,577			3,952			—			17,777
Gross profit		26,321			12,848			10,396			605			50,170
Selling and administrative expenses		14,012			5,618			7,198			1,300			28,128
Income (loss) from operations		12,309			7,230			3,198			(695	)		22,042
Interest (expense) income allocation		(1,676	)		(683	)		(775	)		142			(2,992	)
Income (loss) before provision for income taxes		10,633			6,515			2,423			(553	)		19,018
Rental equipment acquisitions		8,233			15,532			927			—			24,692
Accounts receivable, net (period end)		55,883			19,902			16,490			5,817			98,092
Rental equipment, at cost (period end)		779,839			269,043			310,478		—				1,359,360
Rental equipment, net book value (period end)		544,707			114,799			205,832		—				865,338
Utilization (period end) ²		76.9	%		63.5	%		57.5	%
Average utilization ²		77.3	%		62.7	%		57.6	%

Gross Enviroplex sales revenues were $2,805 and $2,813 for the three months ended March 31, 2019 and 2018, respectively. There were $795 inter-segment sales to Mobile Modular in the three months ended March 31, 2018, which required elimination in consolidation. There were no inter-segment sales in the three months ended March 31, 2019.

Utilization is calculated each month by dividing the cost of rental equipment on rent by the total cost of rental equipment excluding accessory equipment and for Mobile Modular and Adler Tanks excluding new equipment inventory. The Average utilization for the period is calculated using the average costs of rental equipment.

No single customer accounted for more than 10% of total revenues for the three months ended March 31, 2019 and 2018. Revenues from foreign country customers accounted for 3% and 4%, respectively, of the Company’s total revenues for the same periods.