Securities Available for Sale - Non-Agency Collateralized Mortgage Obligations (Details) (USD $)	6 Months Ended
	Mar. 31, 2015	Sep. 30, 2014
Financing Receivable, Recorded Investment [Line Items]
Amortized Cost	$ 182,124,600
Market value	182,981,526	188,743,273
Collateralized Mortgage Obligations
Financing Receivable, Recorded Investment [Line Items]
Cumulative net impairment losses recognized in earnings	380,000
Current par value	10,853,000
Amortized Cost	10,471,000
Market value	10,357,000
Unrealized gain (loss)	(114,000)
Collateralized Mortgage Obligations | GSR 2003-4F 1A2
Financing Receivable, Recorded Investment [Line Items]
Current par value	163,000
Amortized Cost	163,000
Market value	166,000
Unrealized gain (loss)	3,000
Collateralized Mortgage Obligations | MASTR 2003-8 4A1
Financing Receivable, Recorded Investment [Line Items]
Current par value	214,000
Amortized Cost	213,000
Market value	216,000
Unrealized gain (loss)	3,000
Collateralized Mortgage Obligations | SARM 2004-6 3A3
Financing Receivable, Recorded Investment [Line Items]
Current par value	831,000
Amortized Cost	831,000
Market value	786,000
Unrealized gain (loss)	(45,000)
Collateralized Mortgage Obligations | CMLTI 2004-HYB1 A31
Financing Receivable, Recorded Investment [Line Items]
Current par value	1,035,000
Amortized Cost	1,035,000
Market value	1,031,000
Unrealized gain (loss)	(4,000)
Collateralized Mortgage Obligations | MARM 2004-13 B1
Financing Receivable, Recorded Investment [Line Items]
Current par value	3,406,000
Amortized Cost	3,026,000
Market value	3,007,000
Unrealized gain (loss)	(19,000)
Collateralized Mortgage Obligations | MARM 2004-15 4A1
Financing Receivable, Recorded Investment [Line Items]
Current par value	1,718,000
Amortized Cost	1,718,000
Market value	1,648,000
Unrealized gain (loss)	(70,000)
Collateralized Mortgage Obligations | MARM 2004-7 5A1
Financing Receivable, Recorded Investment [Line Items]
Current par value	3,486,000
Amortized Cost	3,485,000
Market value	3,503,000
Unrealized gain (loss)	18,000
Investment Grade | Collateralized Mortgage Obligations
Financing Receivable, Recorded Investment [Line Items]
Cumulative net impairment losses recognized in earnings	0
Current par value	1,208,000
Amortized Cost	1,207,000
Market value	1,168,000
Unrealized gain (loss)	(39,000)
Investment Grade | Collateralized Mortgage Obligations | GSR 2003-4F 1A2
Financing Receivable, Recorded Investment [Line Items]
Cumulative net impairment losses recognized in earnings	0
Investment Grade | Collateralized Mortgage Obligations | MASTR 2003-8 4A1
Financing Receivable, Recorded Investment [Line Items]
Cumulative net impairment losses recognized in earnings	0
Investment Grade | Collateralized Mortgage Obligations | SARM 2004-6 3A3
Financing Receivable, Recorded Investment [Line Items]
Cumulative net impairment losses recognized in earnings	0
Split Rating | Collateralized Mortgage Obligations
Financing Receivable, Recorded Investment [Line Items]
Cumulative net impairment losses recognized in earnings	0
Current par value	1,035,000
Amortized Cost	1,035,000
Market value	1,031,000
Unrealized gain (loss)	(4,000)
Split Rating | Collateralized Mortgage Obligations | CMLTI 2004-HYB1 A31
Financing Receivable, Recorded Investment [Line Items]
Cumulative net impairment losses recognized in earnings	0
Non-Investment Grade | Collateralized Mortgage Obligations
Financing Receivable, Recorded Investment [Line Items]
Cumulative net impairment losses recognized in earnings	380,000
Current par value	8,610,000
Amortized Cost	8,229,000
Market value	8,158,000
Unrealized gain (loss)	(71,000)
Non-Investment Grade | Collateralized Mortgage Obligations | MARM 2004-13 B1
Financing Receivable, Recorded Investment [Line Items]
Credit rating	NR
Cumulative net impairment losses recognized in earnings	380,000
Non-Investment Grade | Collateralized Mortgage Obligations | MARM 2004-15 4A1
Financing Receivable, Recorded Investment [Line Items]
Cumulative net impairment losses recognized in earnings	0
Non-Investment Grade | Collateralized Mortgage Obligations | MARM 2004-7 5A1
Financing Receivable, Recorded Investment [Line Items]
Cumulative net impairment losses recognized in earnings	$ 0
Fitch, A Rating | Investment Grade | Collateralized Mortgage Obligations | MASTR 2003-8 4A1
Financing Receivable, Recorded Investment [Line Items]
Credit rating	A
Fitch, BBB Rating | Investment Grade | Collateralized Mortgage Obligations | GSR 2003-4F 1A2
Financing Receivable, Recorded Investment [Line Items]
Credit rating	BBB
Fitch, BBB Rating | Split Rating | Collateralized Mortgage Obligations | CMLTI 2004-HYB1 A31
Financing Receivable, Recorded Investment [Line Items]
Credit rating	BBB
Fitch, B Rating | Non-Investment Grade | Collateralized Mortgage Obligations | MARM 2004-15 4A1
Financing Receivable, Recorded Investment [Line Items]
Credit rating	B
Fitch, n/a Rating | Investment Grade | Collateralized Mortgage Obligations | SARM 2004-6 3A3
Financing Receivable, Recorded Investment [Line Items]
Credit rating	n/a
Fitch, n/a Rating | Non-Investment Grade | Collateralized Mortgage Obligations | MARM 2004-13 B1
Financing Receivable, Recorded Investment [Line Items]
Credit rating	n/a
Fitch, n/a Rating | Non-Investment Grade | Collateralized Mortgage Obligations | MARM 2004-7 5A1
Financing Receivable, Recorded Investment [Line Items]
Credit rating	n/a
Standard & Poor's, AA Plus Rating | Investment Grade | Collateralized Mortgage Obligations | GSR 2003-4F 1A2
Financing Receivable, Recorded Investment [Line Items]
Credit rating	AA+
Standard & Poor's, A Plus Rating | Investment Grade | Collateralized Mortgage Obligations | MASTR 2003-8 4A1
Financing Receivable, Recorded Investment [Line Items]
Credit rating	A+
Standard & Poor's, A Plus Rating | Investment Grade | Collateralized Mortgage Obligations | SARM 2004-6 3A3
Financing Receivable, Recorded Investment [Line Items]
Credit rating	A+
Standard & Poor's, BB Rating | Non-Investment Grade | Collateralized Mortgage Obligations | MARM 2004-7 5A1
Financing Receivable, Recorded Investment [Line Items]
Credit rating	BB
Standard & Poor's, CCC Rating | Non-Investment Grade | Collateralized Mortgage Obligations | MARM 2004-13 B1
Financing Receivable, Recorded Investment [Line Items]
Credit rating	CCC
Standard & Poor's, n/a Rating | Split Rating | Collateralized Mortgage Obligations | CMLTI 2004-HYB1 A31
Financing Receivable, Recorded Investment [Line Items]
Credit rating	n/a
Standard & Poor's, n/a Rating | Non-Investment Grade | Collateralized Mortgage Obligations | MARM 2004-15 4A1
Financing Receivable, Recorded Investment [Line Items]
Credit rating	n/a
Moody's, Ba3 Rating | Split Rating | Collateralized Mortgage Obligations | CMLTI 2004-HYB1 A31
Financing Receivable, Recorded Investment [Line Items]
Credit rating	Ba3
Moody's, Ba3 Rating | Non-Investment Grade | Collateralized Mortgage Obligations | MARM 2004-7 5A1
Financing Receivable, Recorded Investment [Line Items]
Credit rating	Ba3
Moody's, B3 Rating | Non-Investment Grade | Collateralized Mortgage Obligations | MARM 2004-15 4A1
Financing Receivable, Recorded Investment [Line Items]
Credit rating	B3
Moody's, n/a Rating | Investment Grade | Collateralized Mortgage Obligations | GSR 2003-4F 1A2
Financing Receivable, Recorded Investment [Line Items]
Credit rating	n/a
Moody's, n/a Rating | Investment Grade | Collateralized Mortgage Obligations | MASTR 2003-8 4A1
Financing Receivable, Recorded Investment [Line Items]
Credit rating	n/a
Moody's, n/a Rating | Investment Grade | Collateralized Mortgage Obligations | SARM 2004-6 3A3
Financing Receivable, Recorded Investment [Line Items]
Credit rating	n/a