Derivative Instruments and Other Hedging Activities - Effect of Hedging Instruments on Consolidated Financial Statements (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Designated as Hedging Instruments | Cash Flow Hedging | Interest rate contracts | Interest expense
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in OCI, net of taxes	$ 2,549	$ 73
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income, net of taxes	(116)	(45)
Amount of Gain (Loss) Recognized in Income on Derivative (Amount Excluded from Effectiveness Testing)	0	0
Not Designated as Hedging Instruments
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in Income on Derivatives	5,086	1,423
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	1,049	1,117
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	5	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	3,387	(360)
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	648	655
Not Designated as Hedging Instruments | Other contracts | Other income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in Income on Derivatives	$ (3)	$ 4