Segment Reporting - Summarized Financial Information for Company's Reportable Segments (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017		Dec. 31, 2017
Segment Reporting Information [Line Items]
Rental revenues		$ 82,155	$ 73,781	$ 233,683		$ 211,712
Rental related services revenues		23,880	21,856	60,797		58,587
Sales and other revenues				70,735		69,508
Total revenues		143,147	135,388	365,215		339,807
Depreciation of rental equipment		18,407	17,492	54,287		52,113
Gross profit		64,050	58,775	168,148		151,656
Selling and administrative expenses		28,226	28,489	85,833		83,702
Income from operations		35,824	30,286	82,315		67,954
Interest (expense) income allocation				(9,133)		(8,724)
Income before provision for income taxes		32,553	27,336	72,677		59,503
Rental equipment acquisitions				95,635		76,937
Accounts receivable, net (period end)		115,089	107,413	115,089		107,413		$ 105,872
Rental equipment, at cost (period end)		1,398,263	1,350,493	1,398,263		1,350,493		1,347,533
Rental equipment, net book value (period end)		888,607	865,724	888,607		865,724		$ 862,320
Mobile Modular [Member]
Segment Reporting Information [Line Items]
Rental revenues				116,436		104,923
Rental related services revenues				40,510		38,283
Sales and other revenues				31,667		30,622
Total revenues		74,891	68,887	188,613		173,828
Depreciation of rental equipment				15,841		15,951
Gross profit				86,515		77,939
Selling and administrative expenses				43,191		42,157
Income from operations				43,324		35,782
Interest (expense) income allocation				(5,256)		(5,008)
Income before provision for income taxes				38,068		30,774
Rental equipment acquisitions				40,704		28,107
Accounts receivable, net (period end)		69,419	66,126	69,419		66,126
Rental equipment, at cost (period end)		801,129	781,791	801,129		781,791
Rental equipment, net book value (period end)		558,790	547,115	$ 558,790		$ 547,115
Utilization (period end)	[1]			79.20%		76.80%
Average utilization	[1]			77.80%		76.60%
TRS-RenTelco [Member]
Segment Reporting Information [Line Items]
Rental revenues				$ 65,919		$ 60,569
Rental related services revenues				2,287		2,095
Sales and other revenues				18,321		16,493
Total revenues		28,137	27,304	86,527		79,157
Depreciation of rental equipment				26,536		24,335
Gross profit				40,155		36,420
Selling and administrative expenses				16,780		16,475
Income from operations				23,375		19,945
Interest (expense) income allocation				(1,999)		(1,726)
Income before provision for income taxes				20,871		18,492
Rental equipment acquisitions				51,744		45,700
Accounts receivable, net (period end)		18,991	16,253	18,991		16,253
Rental equipment, at cost (period end)		284,647	258,877	284,647		258,877
Rental equipment, net book value (period end)		129,816	106,728	$ 129,816		$ 106,728
Utilization (period end)	[1]			61.50%		64.30%
Average utilization	[1]			62.40%		62.80%
Adler Tanks [Member]
Segment Reporting Information [Line Items]
Rental revenues				$ 51,328		$ 46,220
Rental related services revenues				18,000		18,209
Sales and other revenues				916		1,701
Total revenues		26,017	23,416	70,244		66,130
Depreciation of rental equipment				11,910		11,827
Gross profit				35,031		31,407
Selling and administrative expenses				22,245		21,855
Income from operations				12,786		9,552
Interest (expense) income allocation				(2,409)		(2,301)
Income before provision for income taxes				10,377		7,251
Rental equipment acquisitions				3,187		3,130
Accounts receivable, net (period end)		19,876	18,118	19,876		18,118
Rental equipment, at cost (period end)		312,487	309,825	312,487		309,825
Rental equipment, net book value (period end)		200,001	211,881	$ 200,001		$ 211,881
Utilization (period end)	[1]			64.00%		59.70%
Average utilization	[1]			59.80%		54.70%
Enviroplex [Member]
Segment Reporting Information [Line Items]
Sales and other revenues	[2]			$ 19,831		$ 20,692
Total revenues		14,102	15,781	19,831	[2]	20,692	[2]
Gross profit	[2]			6,447		5,890
Selling and administrative expenses	[2]			3,617		3,215
Income from operations	[2]			2,830		2,675
Interest (expense) income allocation	[2]			531		311
Income before provision for income taxes	[2]			3,361		2,986
Accounts receivable, net (period end)	[2]	$ 6,803	$ 6,916	$ 6,803		$ 6,916

[1] 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.

[2] Gross Enviroplex sales revenues were $21,191 and $20,692 for the nine months ended September 30, 2018 and 2017, respectively. There were $1,360 inter-segment sales to Mobile Modular in the nine months ended September 30, 2018, which required elimination in consolidation. There were no inter-segment sales in the nine months ended September 30, 2017.