Securities Available for Sale (Tables)

6 Months Ended

Mar. 31, 2020

Investments, Debt and Equity Securities [Abstract]

Schedule of amortized cost and fair value of investments by contractual maturity

The amortized cost and approximate fair value of investments in securities, all of which are classified as available for sale according to management’s intent, are summarized as follows.

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
	(dollars in thousands)
As of March 31, 2020
U.S. Treasury securities	$	69,629	$	954	$	—	$	70,583
Mortgage-backed securities:
Government National Mortgage Association	566,747		11,340		(733)		577,354
Federal Home Loan Mortgage Corporation	556,535		15,747		(731)		571,551
Federal National Mortgage Association	386,996		15,337		(27)		402,306
Small Business Assistance Program	300,498		5,725		(42)		306,181
States and political subdivision securities	60,511		517		(27)		61,001
Other	1,006		45		—		1,051
Total	$	1,941,922	$	49,665	$	(1,560)	$	1,990,027

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
	(dollars in thousands)
As of September 30, 2019
U.S. Treasury securities	$	94,178	$	599	$	(32)	$	94,745
Mortgage-backed securities:
Government National Mortgage Association	501,139		3,374		(3,027)		501,486
Federal Home Loan Mortgage Corporation	463,974		8,840		(770)		472,044
Federal National Mortgage Association	322,340		5,409		(398)		327,351
Small Business Assistance Program	316,502		3,674		(154)		320,022
States and political subdivision securities	66,145		494		(116)		66,523
Other	1,006		31		—		1,037
Total	$	1,765,284	$	22,421	$	(4,497)	$	1,783,208

The amortized cost and approximate fair value of debt securities available for sale as of March 31, 2020 and September 30, 2019, by contractual maturity, are shown below. Maturities of mortgage-backed securities may differ from contractual maturities because the mortgages underlying the securities may be called or repaid without penalty.

	March 31, 2020				September 30, 2019
	Amortized  Cost		Estimated Fair Value		Amortized  Cost		Estimated Fair Value
	(dollars in thousands)
Due in one year or less	$	82,615	$	83,577	$	58,377	$	58,343
Due after one year through five years	35,858		36,102		89,836		90,601
Due after five years through ten years	11,667		11,905		12,110		12,324
Due after ten years	—		—		—		—
	130,140		131,584		160,323		161,268
Mortgage-backed securities	1,810,776		1,857,392		1,603,955		1,620,903
Securities without contractual maturities	1,006		1,051		1,006		1,037
Total	$	1,941,922	$	1,990,027	$	1,765,284	$	1,783,208

Schedule of gross unrealized losses on investments

The following table presents the Company’s gross unrealized losses and approximate fair value in investments, aggregated by investment category and length of time that individual securities have been in a continuous unrealized loss position.

	Less than 12 months				12 months or more				Total
	Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
	(dollars in thousands)
As of March 31, 2020
U.S. Treasury securities	$	—	$	—	$	—	$	—	$	—	$	—
Mortgage-backed securities	30,374		(189)		207,955		(1,344)		238,329		(1,533)
States and political subdivision securities	—		—		9,242		(27)		9,242		(27)
Other	—		—		—		—		—		—
Total	$	30,374	$	(189)	$	217,197	$	(1,371)	$	247,571	$	(1,560)

	Less than 12 months				12 months or more				Total
	Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses		Estimated Fair Value		Unrealized Losses
	(dollars in thousands)
As of September 30, 2019
U.S. Treasury securities	$	—	$	—	$	44,729	$	(32)	$	44,729	$	(32)
Mortgage-backed securities	94,612		(205)		474,979		(4,144)		569,591		(4,349)
States and political subdivision securities	—		—		23,693		(116)		23,693		(116)
Other	—		—		—		—		—		—
Total	$	94,612	$	(205)	$	543,401	$	(4,292)	$	638,013	$	(4,497)