Quarterly Financial Data (Unaudited) - Summary of Unaudited Quarterly Results (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 17,364	$ 15,914	$ 14,415	$ 14,205	$ 15,336	$ 14,616	$ 13,604	$ 13,883	$ 61,898	$ 57,439	$ 56,132
Operating income from continuing operations	4,266	5,857	3,932	5,034	5,434	5,333	3,480	4,329	19,089	18,576	18,820
Income from continuing operations	1,358	3,924	3,051	3,614	2,444	3,674	2,459	3,630	11,947	12,207	14,579
Loss from discontinued operations					(100)	(76)				(176)	588
Net income	$ 1,358	$ 3,924	$ 3,051	$ 3,614	$ 2,344	$ 3,598	$ 2,459	$ 3,630	$ 11,947	$ 12,031	$ 15,167
Basic income (loss) per share:
Continuing operations	$ 0.10	$ 0.30	$ 0.24	$ 0.27	$ 0.18	$ 0.27	$ 0.18	$ 0.26	$ 0.92	$ 0.90	$ 1.01
Discontinued operations	0.00	0.00	0.00	0.00	(0.01)	(0.01)	0.00	0.00	0.00	(0.01)	0.04
Net income	0.10	0.30	0.24	0.27	0.17	0.26	0.18	0.26	0.92	0.88	1.05
Diluted income (loss) per share:
Continuing operations	0.10	0.30	0.23	0.27	0.18	0.27	0.18	0.26	0.90	0.88	0.99
Discontinued operations	0.00	0.00	0.00	0.00	(0.01)	(0.01)	0.00	0.00	0.00	(0.01)	0.04
Net income	$ 0.10	$ 0.30	$ 0.23	$ 0.27	$ 0.17	$ 0.26	$ 0.18	$ 0.26	$ 0.90	$ 0.87	$ 1.03