Quarterly Financial Information - Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operations Data
Rental revenues	$ 70,352	$ 67,757	$ 66,747	$ 66,532	$ 70,694	$ 70,195	$ 67,305	$ 65,502	$ 271,388	$ 273,696	$ 269,575
Total revenues	105,283	121,993	103,105	93,699	105,282	113,048	96,026	90,188	424,080	404,544	408,122
Gross profit	49,323	50,433	43,756	40,655	46,756	50,146	40,918	39,087	184,167	176,907	182,219
Income from operations	22,696	24,232	18,073	14,258	21,467	25,150	16,465	13,875	79,259	76,957	85,360
Income before provision for income taxes	19,795	21,277	15,006	10,853	18,523	22,505	14,033	11,316	66,931	66,377	76,561
Net income	$ 9,734	$ 12,872	$ 9,079	$ 6,566	$ 11,518	$ 13,616	$ 8,490	$ 6,846	$ 38,251	$ 40,470	$ 45,709
Earnings per share:
Basic	$ 0.41	$ 0.54	$ 0.38	$ 0.28	$ 0.48	$ 0.54	$ 0.33	$ 0.26	$ 1.60	$ 1.60	$ 1.77
Diluted	0.40	0.54	0.38	0.27	0.48	0.54	0.32	0.26	1.60	1.59	1.75
Dividends declared per share	$ 0.255	$ 0.255	$ 0.255	$ 0.255	$ 0.250	$ 0.250	$ 0.250	$ 0.250	$ 1.02	$ 1.00	$ 0.98
Shares used in per share calculations:
Basic	23,927	23,911	23,900	23,862	23,932	25,334	26,142	26,091	23,900	25,369	25,914
Diluted	24,123	24,041	23,949	23,911	24,015	25,408	26,273	26,276	23,976	25,457	26,175
Balance Sheet Data
Rental equipment, net	$ 856,371	$ 862,528	$ 868,422	$ 867,215	$ 869,601	$ 864,277	$ 856,489	$ 839,078	$ 856,371	$ 869,601	$ 825,750
Total assets	1,128,276	1,144,923	1,148,018	1,132,355	1,152,549	1,149,095	1,132,750	1,112,056	1,128,276	1,152,549
Notes payable	326,266	345,286	363,121	365,772	381,281	382,113	337,177	320,923	326,266	381,281
Shareholders' equity	$ 394,287	$ 390,600	$ 383,313	$ 380,512	$ 379,687	$ 389,464	$ 426,823	$ 425,848	$ 394,287	$ 379,687	$ 424,531	$ 401,030