Segment Reporting - Summarized Financial Information for Company's Reportable Segments (Detail) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Rental revenues		$ 88,517	$ 88,138	$ 85,629	$ 89,506	$ 92,231	$ 90,857	$ 88,105	$ 82,696	$ 351,790	$ 353,889	$ 318,774
Rental related services revenues										92,393	101,038	82,907
Sales and other revenues										128,371	115,303	96,649
Total revenues		148,980	156,448	137,673	129,453	147,221	173,562	127,439	122,008	572,554	570,230	498,330
Depreciation of rental equipment										85,866	80,391	73,139
Gross profit		70,654	68,204	63,232	61,656	70,997	78,282	59,881	57,005	263,746	266,165	233,251
Selling and administrative expenses										122,993	124,793	115,770
Income from operations		41,026	37,333	32,692	29,702	38,248	46,748	29,066	27,310	140,753	141,372	117,481
Interest expense (income) allocation										8,787	12,331	12,297
Income before provision/benefit for income taxes		39,310	35,495	30,625	26,614	35,454	43,455	25,965	24,251	132,044	129,125	104,695
Rental equipment acquisitions										84,207	170,018	134,098
Accounts receivable, net (period end)		123,316				128,099				123,316	128,099	121,016
Rental equipment, at cost (period end)		1,530,841				1,520,411				1,530,841	1,520,411	1,416,000
Rental equipment, net book value (period end)		938,116	$ 948,125	$ 969,681	$ 975,709	967,500	$ 958,610	$ 943,152	$ 912,878	938,116	967,500	901,015
Mobile Modular [Member]
Segment Reporting Information [Line Items]
Rental revenues										188,719	182,316	159,136
Rental related services revenues										67,527	69,395	54,696
Sales and other revenues										65,278	49,299	40,742
Total revenues										321,524	301,010	254,574
Depreciation of rental equipment										22,967	22,071	21,200
Gross profit										155,874	143,618	120,750
Selling and administrative expenses										68,470	65,699	58,017
Income from operations										87,404	77,919	62,733
Interest expense (income) allocation										5,104	7,946	7,132
Income before provision/benefit for income taxes										82,300	69,973	55,601
Rental equipment acquisitions										39,078	75,433	63,374
Accounts receivable, net (period end)		81,640				83,182				81,640	83,182	72,295
Rental equipment, at cost (period end)		882,115				868,807				882,115	868,807	817,375
Rental equipment, net book value (period end)		611,590				610,048				$ 611,590	$ 610,048	$ 572,032
Utilization (period end)	[1]									76.00%	79.10%	79.30%
Average utilization	[1]									77.20%	79.20%	78.20%
TRS-RenTelco [Member]
Segment Reporting Information [Line Items]
Rental revenues										$ 109,083	$ 103,704	$ 89,937
Rental related services revenues										3,080	3,260	3,300
Sales and other revenues										28,648	24,519	25,420
Total revenues										140,811	131,483	118,657
Depreciation of rental equipment										46,472	41,948	36,011
Gross profit										60,864	60,748	54,773
Selling and administrative expenses										24,306	24,645	22,823
Income from operations										36,558	36,103	31,950
Interest expense (income) allocation										2,133	1,970	2,696
Income before provision/benefit for income taxes										34,503	34,217	28,765
Rental equipment acquisitions										42,588	89,759	65,467
Accounts receivable, net (period end)		22,735				23,788				22,735	23,788	20,732
Rental equipment, at cost (period end)		333,020				335,343				333,020	335,343	285,052
Rental equipment, net book value (period end)		156,536				172,413				$ 156,536	$ 172,413	$ 131,450
Utilization (period end)	[1]									67.40%	64.50%	62.10%
Average utilization	[1]									66.20%	66.20%	62.70%
Adler Tanks [Member]
Segment Reporting Information [Line Items]
Rental revenues										$ 53,988	$ 67,869	$ 69,701
Rental related services revenues										21,786	28,383	24,911
Sales and other revenues										1,708	1,671	1,441
Total revenues										77,482	97,923	96,053
Depreciation of rental equipment										16,427	16,372	15,928
Gross profit										34,079	47,014	48,055
Selling and administrative expenses										24,764	29,321	30,026
Income from operations										9,315	17,693	18,029
Interest expense (income) allocation										2,107	3,436	3,252
Income before provision/benefit for income taxes										7,208	14,257	14,777
Rental equipment acquisitions										2,541	4,826	5,257
Accounts receivable, net (period end)		13,655				17,281				13,655	17,281	19,992
Rental equipment, at cost (period end)		315,706				316,261				315,706	316,261	313,573
Rental equipment, net book value (period end)		169,990				185,039				$ 169,990	$ 185,039	$ 197,533
Utilization (period end)	[1]									39.80%	48.40%	56.40%
Average utilization	[1]									44.60%	54.70%	59.90%
Enviroplex [Member]
Segment Reporting Information [Line Items]
Sales and other revenues	[2]									$ 32,737	$ 39,814	$ 29,046
Total revenues	[2]									32,737	39,814	29,046
Gross profit	[2]									12,929	14,785	9,673
Selling and administrative expenses	[2]									5,453	5,128	4,904
Income from operations	[2]									7,476	9,657	4,769
Interest expense (income) allocation	[2]									(557)	(1,021)	(783)
Income before provision/benefit for income taxes	[2]									8,033	10,678	5,552
Accounts receivable, net (period end)	[2]	$ 5,286				$ 3,848				$ 5,286	$ 3,848	$ 7,997

[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 $34,014, $39,814 and $30,407 in 2020, 2019 and 2018, respectively.  There were $1,277 and $1,361 inter-segment sales to Mobile Modular in 2020 and 2018, which have been eliminated in consolidation.  There were no inter-segment sales in 2019.