Derivative Instruments and Other Hedging Activities - Effect of Hedging Instruments on Consolidated Financial Statements (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Designated as Hedging Instruments \| Cash Flow Hedging \| Interest rate contracts \| Interest expense
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized	$ (22)	$ (101)	$ (178)	$ (249)
Amount of Gain (Loss) Recognized in Income on Derivatives (Amount Excluded from Effectiveness Testing)	0	0	0	0
Not Designated as Hedging Instruments
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized	2,850	(1,694)	10,142	(2,072)
Not Designated as Hedging Instruments \| Interest rate contracts \| Other income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized	2,586	743	5,093	3,159
Not Designated as Hedging Instruments \| Foreign exchange contracts \| Other income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized	7	24	17	38
Not Designated as Hedging Instruments \| Forward sales contracts \| Mortgage income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized	948	(2,007)	4,563	(3,893)
Not Designated as Hedging Instruments \| Written and purchased options \| Mortgage income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized	(692)	(462)	473	(1,393)
Not Designated as Hedging Instruments \| Other contracts \| Other income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized	1	8	(4)	17
OCI \| Designated as Hedging Instruments \| Cash Flow Hedging \| Interest rate contracts
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized	$ 818	$ (158)	$ 4,762	$ (1,081)

Amount of gain (loss) from excluded component of derivative hedge, recognized in earnings. Excludes recognition under systematic and rational method.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 20
-Section 45
-Paragraph 1A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109974929&loc=SL110061172-113977

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959

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