Quarterly Consolidated Financial Data (Detail) (USD $)	3 Months Ended												12 Months Ended
	Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013	Sep. 30, 2012		Sep. 30, 2011
Quarterly Financial Information [Line Items]
Operating revenues	$ 69,673,000	[1]	$ 75,647,000	[1]	$ 83,350,000	$ 76,629,000	$ 72,998,000	[1]	$ 68,348,000	[1]	$ 85,546,000	$ 92,382,000	$ 305,299,000	$ 319,274,000		$ 333,279,000
Income (loss) from operations	(2,463,000)	[1]	6,851,000	[1]	10,598,000	5,194,000	2,131,000	[1]	1,798,000	[1]	9,446,000	3,226,000	20,180,000	16,601,000		(3,326,000)
Net income (loss)	$ (2,790,000)	[1]	$ 4,063,000	[1]	$ 6,279,000	$ 2,928,000	$ 1,152,000	[1]	$ 1,141,000	[1]	$ 5,589,000	$ 3,231,000	$ 10,480,000	$ 11,113,000	[2]	$ (3,246,000)
Basic income (loss) per share attributable to common stock	$ (0.35)	[1]	$ 0.50	[1]	$ 0.78	$ 0.36	$ 0.14	[1]	$ 0.14	[1]	$ 0.71	$ 0.41	$ 1.31	$ 1.40	[2]	$ (0.42)
Diluted income (loss) per share attributable to common stock	$ (0.35)	[1]	$ 0.50	[1]	$ 0.78	$ 0.36	$ 0.14	[1]	$ 0.14	[1]	$ 0.70	$ 0.41	$ 1.31	$ 1.39	[2]	$ (0.42)

[1] The June 30, 2012 and September 30, 2012 earnings per share calculations have been adjusted for the two-class method to reflect restricted shares that were not reflected as participating in the prior period. Basic earnings per share as previously reported for the quarters ended June 30, 2012 and September 30, 2012 were both $0.15. Diluted earnings per share as previously reported for the quarter ended September 30, 2012 was $0.15. The impact on all prior period financial statements is deemed immaterial.

[2] The 2012 earnings per share calculations have been adjusted for the two-class method to reflect restricted shares that were not reflected as participating in the prior period. Basic earnings per share as previously reported for year ended September 30, 2012 was $1.42. Diluted earnings per share as previously reported for the year-ended September 30, 2012 was $1.40. Basic weighted average shares outstanding as previously reported for the year ended September 30, 2012 was 7,841,722. Diluted weighted average shares outstanding as previously reported for the year ended September 30, 2012 was 7,931,593. The impact on all prior period financial statements is deemed immaterial.