Investment Securities - Continuous Unrealized Loss Position of Held-to-Maturity Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017
Investment securities held-to-maturity:
Less than 12 months, Fair Value	$ 204,393	$ 29,965
Less than 12 months, Gross unrealized (losses)	(2,978)	(349)
12 months or longer, Fair value	30,046	99,476
12 months or longer, Gross unrealized (losses)	(515)	(768)
Total, Fair value	234,439	129,441
Total, Gross unrealized (losses)	(3,493)	(1,117)
U.S. government and agency obligations
Investment securities held-to-maturity:
Less than 12 months, Fair Value	8,344	0
Less than 12 months, Gross unrealized (losses)	(58)	0
12 months or longer, Fair value	0	3,400
12 months or longer, Gross unrealized (losses)	0	(7)
Total, Fair value	8,344	3,400
Total, Gross unrealized (losses)	(58)	(7)
Mortgage-backed securities and collateralized mortgage obligations
Investment securities held-to-maturity:
Less than 12 months, Fair Value	196,049	29,965
Less than 12 months, Gross unrealized (losses)	(2,920)	(349)
12 months or longer, Fair value	30,046	96,076
12 months or longer, Gross unrealized (losses)	(515)	(761)
Total, Fair value	226,095	126,041
Total, Gross unrealized (losses)	$ (3,435)	$ (1,110)

Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity that have been in a continuous loss position for twelve months or longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity in a continuous loss position.

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Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity that have been in a continuous loss position for less than twelve months.

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This item represents the fair value of securities categorized as held-to-maturity that have been in a continuous unrealized loss position for less than twelve months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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This item represents the fair value of securities categorized as held-to-maturity securities that have been in a continuous unrealized loss position for twelve months or longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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