Quarterly Financial Data - Summary of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Quarterly Financial Information Disclosure [Abstract]
Net revenues	$ 53,100	$ 51,737	$ 56,451	$ 52,283	$ 49,697	$ 50,140	$ 54,125	$ 46,809	$ 213,571	$ 200,771	$ 196,082
Gross profit	32,150	31,956	34,569	31,786	30,630	31,146	33,477	29,039	130,461	124,292	127,212
Net earnings	$ 5,434	$ 6,825	$ 5,288	$ 6,302	$ 5,726	$ 240	$ 9,312	$ 6,279	$ 23,849	$ 21,557	$ 32,229
Basic earnings per common share	$ 0.13	$ 0.16	$ 0.12	$ 0.15	$ 0.14	$ 0.01	$ 0.22	$ 0.15	$ 0.56	$ 0.51	$ 0.77
Diluted earnings per common share	0.13	0.16	0.12	0.15	0.13	0.01	0.22	0.15	0.56	0.51	0.76
Cash dividends per common share	$ 0.125	$ 0.125	$ 0.125	$ 0.125	$ 0.125	$ 0.125	$ 0.125	$ 0.200	$ 0.500	$ 0.575	$ 0.800