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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Designated as Hedging Instruments | Cash Flow Hedging | Interest rate contracts | Other income (expense)
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in OCI net of taxes (Effective Portion)	$ (158)	$ 146	$ (1,081)	$ (6,309)
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income net of taxes (Effective Portion)	(101)	0	(249)	0
Amount of Gain (Loss) Recognized in Income on Derivative (Ineffective Portion and 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 in Income on Derivatives	(1,694)	(2,995)	(2,072)	(1,358)
Not Designated as Hedging Instruments | Interest rate contracts | Other income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in Income on Derivatives	743	2,215	3,159	7,509
Not Designated as Hedging Instruments | Foreign exchange contracts | Other income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in Income on Derivatives	24	4	38	7
Not Designated as Hedging Instruments | Forward sales contracts | Mortgage income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in Income on Derivatives	(2,007)	(2,590)	(3,893)	(12,720)
Not Designated as Hedging Instruments | Written and purchased options | Mortgage income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in Income on Derivatives	(462)	(2,624)	(1,393)	3,846
Not Designated as Hedging Instruments | Other contracts | Other income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in Income on Derivatives	$ 8	$ 0	$ 17	$ 0