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Loans Held for Sale, at Fair Value - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accounts Notes And Loans Receivable [Line Items]
Maximum number of days loans held for sale are typically sold	45 days
Loans held for sale in nonaccrual status	$ 0	$ 0
Recognized gain from change in fair value on loans held for sale	15,100,000	2,100,000
Interest Income [Member]
Accounts Notes And Loans Receivable [Line Items]
Interest income on Loans held for sale	4,700,000	6,500,000
Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans held for sale past due	$ 0	$ 0

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- Definition

Maximum period of loans held for sale sold.

+ References

No definition available.

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- Definition

For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14172-108612

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- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524

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- Definition

Recorded Investment in financing receivables that are past due at the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953401-111524

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- Definition

Interest and fee income from mortgage loans considered to be held-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.1)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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