Segment Reporting - Summarized Financial Information for Company's Reportable Segments (Detail) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Rental revenues		$ 77,705	$ 73,781	$ 69,953	$ 67,978	$ 70,352	$ 67,757	$ 66,747	$ 66,532	$ 289,417	$ 271,388	$ 273,696
Rental related services revenues										78,068	75,859	73,314
Sales and other revenues										94,549	76,833	57,534
Total revenues		122,227	135,388	109,582	94,837	105,283	121,993	103,105	93,699	462,034	424,080	404,544
Depreciation of rental equipment										69,908	72,197	75,213
Gross profit		54,689	58,775	49,211	43,670	49,323	50,433	43,756	40,655	206,345	184,167	176,907
Selling and administrative expenses										111,605	104,908	99,950
Income from operations		26,786	30,286	21,846	15,822	22,696	24,232	18,073	14,258	94,740	79,259	76,957
Interest expense (income) allocation										(11,622)	(12,207)	(10,092)
Income before (benefit) provision for income taxes		23,949	27,336	18,908	13,259	19,795	21,277	15,006	10,853	83,452	66,931	66,377
Rental equipment acquisitions										98,107	74,634	133,378
Accounts receivable, net (period end)		105,872				96,877				105,872	96,877	95,017
Rental equipment, at cost (period end)		1,347,533				1,324,057				1,347,533	1,324,057	1,310,083
Rental equipment, net book value (period end)		862,320	$ 865,724	$ 863,207	$ 856,981	856,371	$ 862,528	$ 868,422	$ 867,215	862,320	856,371	869,601
Mobile Modular [Member]
Segment Reporting Information [Line Items]
Rental revenues										142,584	130,496	115,986
Rental related services revenues										50,448	49,206	45,616
Sales and other revenues										38,234	29,810	22,682
Total revenues										231,266	209,512	184,284
Depreciation of rental equipment										21,247	21,001	19,246
Gross profit										103,935	93,816	78,771
Selling and administrative expenses										55,583	51,432	46,496
Income from operations										48,352	42,384	32,275
Interest expense (income) allocation										(6,671)	(6,804)	(5,363)
Income before (benefit) provision for income taxes										41,681	35,580	26,912
Rental equipment acquisitions										34,526	43,099	79,622
Accounts receivable, net (period end)		59,274				55,916				59,274	55,916	53,550
Rental equipment, at cost (period end)		775,400				744,099				775,400	744,099	736,875
Rental equipment, net book value (period end)		543,857				544,421				$ 543,857	$ 544,421	$ 529,483
Utilization (period end)	[1]									77.80%	77.30%	76.90%
Average utilization	[1]									76.80%	76.60%	75.80%
TRS-RenTelco [Member]
Segment Reporting Information [Line Items]
Rental revenues										$ 82,812	$ 82,307	$ 89,208
Rental related services revenues										2,858	2,846	3,055
Sales and other revenues										22,374	23,464	22,754
Total revenues										108,044	108,617	115,017
Depreciation of rental equipment										32,891	35,256	39,974
Gross profit										50,289	45,797	47,836
Selling and administrative expenses										22,171	21,896	22,930
Income from operations										28,118	23,901	24,906
Interest expense (income) allocation										(2,320)	(2,465)	(2,194)
Income before (benefit) provision for income taxes										26,132	21,315	22,224
Rental equipment acquisitions										58,781	30,505	44,316
Accounts receivable, net (period end)		19,581				19,506				19,581	19,506	21,784
Rental equipment, at cost (period end)		262,325				245,700				262,325	245,700	262,945
Rental equipment, net book value (period end)		109,482				90,172				$ 109,482	$ 90,172	$ 102,191
Utilization (period end)	[1]									61.70%	61.00%	58.70%
Average utilization	[1]									62.90%	60.60%	60.50%
Adler Tanks [Member]
Segment Reporting Information [Line Items]
Rental revenues										$ 64,021	$ 58,585	$ 68,502
Rental related services revenues										24,762	23,807	24,643
Sales and other revenues										2,572	1,438	1,486
Total revenues										91,355	83,830	94,631
Depreciation of rental equipment										15,770	15,940	15,993
Gross profit										43,218	37,409	47,397
Selling and administrative expenses										29,542	27,610	27,494
Income from operations										13,676	9,799	19,903
Interest expense (income) allocation										(3,071)	(3,200)	(2,729)
Income before (benefit) provision for income taxes										10,605	6,599	17,174
Rental equipment acquisitions										4,800	1,030	9,440
Accounts receivable, net (period end)		18,663				16,150				18,663	16,150	17,955
Rental equipment, at cost (period end)		309,808				306,701				309,808	306,701	310,263
Rental equipment, net book value (period end)		208,981				221,778				$ 208,981	$ 221,778	$ 237,927
Utilization (period end)	[1]									57.50%	50.70%	49.70%
Average utilization	[1]									56.00%	50.10%	58.30%
Enviroplex [Member]
Segment Reporting Information [Line Items]
Sales and other revenues	[2]									$ 31,369	$ 22,121	$ 10,612
Total revenues	[2]									31,369	22,121	10,612
Gross profit	[2]									8,903	7,145	2,903
Selling and administrative expenses	[2]									4,309	3,970	3,030
Income from operations	[2]									4,594	3,175	(127)
Interest expense (income) allocation	[2]									440	262	194
Income before (benefit) provision for income taxes	[2]									5,034	3,437	67
Accounts receivable, net (period end)	[2]	$ 8,354				$ 5,305				$ 8,354	$ 5,305	$ 1,728

[1] Utilization is calculated each month by dividing the cost of rental equipment on rent by the total cost of rental equipment excluding new equipment inventory and accessory equipment. The average utilization for the period is calculated using the average costs of rental equipment.

[2] Gross Enviroplex sales revenues were $31,369, $22,206 and $11,530 in 2017, 2016 and 2015, respectively, which includes inter-segment sales to Mobile Modular of $0, $85 and $918, which have been eliminated in consolidation.