Segment Reporting - Summarized Financial Information for Company's Reportable Segments (Detail) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Rental revenues		$ 85,091	$ 82,155	$ 77,267	$ 74,261	$ 77,705	$ 73,781	$ 69,953	$ 67,978	$ 318,774	$ 289,417	$ 271,388
Rental related services revenues										82,907	78,068	75,859
Sales and other revenues										96,649	94,549	76,833
Total revenues		133,115	143,147	116,983	105,085	122,227	135,388	109,582	94,837	498,330	462,034	424,080
Depreciation of rental equipment										73,139	69,908	72,197
Gross profit		65,103	64,050	53,928	50,170	54,689	58,775	49,211	43,670	233,251	206,345	184,167
Selling and administrative expenses										115,770	111,605	104,908
Income from operations		35,166	35,824	24,449	22,042	26,786	30,286	21,846	15,822	117,481	94,740	79,259
Interest expense (income) allocation										(12,297)	(11,622)	(12,207)
Income before provision (benefit) for income taxes		32,018	32,553	21,106	19,018	23,949	27,336	18,908	13,259	104,695	83,452	66,931
Rental equipment acquisitions										134,098	98,107	74,634
Accounts receivable, net (period end)		121,016				105,872				121,016	105,872	96,877
Rental equipment, at cost (period end)		1,416,000				1,347,533				1,416,000	1,347,533	1,324,057
Rental equipment, net book value (period end)		901,015	$ 888,607	$ 876,522	$ 865,338	862,320	$ 865,724	$ 863,207	$ 856,981	901,015	862,320	856,371
Mobile Modular [Member]
Segment Reporting Information [Line Items]
Rental revenues										159,136	142,584	130,496
Rental related services revenues										54,696	50,448	49,206
Sales and other revenues										40,742	38,234	29,810
Total revenues										254,574	231,266	209,512
Depreciation of rental equipment										21,200	21,247	21,001
Gross profit										120,750	103,935	93,816
Selling and administrative expenses										58,017	55,583	51,432
Income from operations										62,733	48,352	42,384
Interest expense (income) allocation										(7,132)	(6,671)	(6,804)
Income before provision (benefit) for income taxes										55,601	41,681	35,580
Rental equipment acquisitions										63,374	34,526	43,099
Accounts receivable, net (period end)		72,295				59,274				72,295	59,274	55,916
Rental equipment, at cost (period end)		817,375				775,400				817,375	775,400	769,190
Rental equipment, net book value (period end)		572,032				543,857				$ 572,032	$ 543,857	$ 544,421
Utilization (period end)	[1]									79.30%	77.80%	77.30%
Average utilization	[1]									78.20%	76.80%	76.60%
TRS-RenTelco [Member]
Segment Reporting Information [Line Items]
Rental revenues										$ 89,937	$ 82,812	$ 82,307
Rental related services revenues										3,300	2,858	2,846
Sales and other revenues										25,420	22,374	23,464
Total revenues										118,657	108,044	108,617
Depreciation of rental equipment										36,011	32,891	35,256
Gross profit										54,773	50,289	45,797
Selling and administrative expenses										22,823	22,171	21,896
Income from operations										31,950	28,118	23,901
Interest expense (income) allocation										(2,696)	(2,320)	(2,465)
Income before provision (benefit) for income taxes										28,765	26,132	21,315
Rental equipment acquisitions										65,467	58,781	30,505
Accounts receivable, net (period end)		20,732				19,581				20,732	19,581	19,506
Rental equipment, at cost (period end)		285,052				262,325				285,052	262,325	246,325
Rental equipment, net book value (period end)		131,450				109,482				$ 131,450	$ 109,482	$ 90,172
Utilization (period end)	[1]									62.10%	61.70%	61.00%
Average utilization	[1]									62.70%	62.90%	60.60%
Adler Tanks [Member]
Segment Reporting Information [Line Items]
Rental revenues										$ 69,701	$ 64,021	$ 58,585
Rental related services revenues										24,911	24,762	23,807
Sales and other revenues										1,441	2,572	1,438
Total revenues										96,053	91,355	83,830
Depreciation of rental equipment										15,928	15,770	15,940
Gross profit										48,055	43,218	37,409
Selling and administrative expenses										30,026	29,542	27,610
Income from operations										18,029	13,676	9,799
Interest expense (income) allocation										(3,252)	(3,071)	(3,200)
Income before provision (benefit) for income taxes										14,777	10,605	6,599
Rental equipment acquisitions										5,257	4,800	1,030
Accounts receivable, net (period end)		19,992				18,663				19,992	18,663	16,150
Rental equipment, at cost (period end)		313,573				309,808				313,573	309,808	308,542
Rental equipment, net book value (period end)		197,533				208,981				$ 197,533	$ 208,981	$ 221,778
Utilization (period end)	[1]									56.40%	57.50%	50.70%
Average utilization	[1]									59.90%	56.00%	50.10%
Enviroplex [Member]
Segment Reporting Information [Line Items]
Sales and other revenues	[2]									$ 29,046	$ 31,369	$ 22,121
Total revenues	[2]									29,046	31,369	22,121
Gross profit	[2]									9,673	8,903	7,145
Selling and administrative expenses	[2]									4,904	4,309	3,970
Income from operations	[2]									4,769	4,594	3,175
Interest expense (income) allocation	[2]									783	440	262
Income before provision (benefit) for income taxes	[2]									5,552	5,034	3,437
Accounts receivable, net (period end)	[2]	$ 7,997				$ 8,354				$ 7,997	$ 8,354	$ 5,305

[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 $30,407, $31,369 and $22,206 in 2018, 2017 and 2016, respectively. There were $1,361 and $85 inter-segment sales to Mobile Modular in 2018 and 2016, respectively, which have been eliminated in consolidation. There were no inter-segment sales in 2017.