Derivative Instruments and Other Hedging Activities - Effect of Hedging Instruments on Consolidated Financial Statements (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 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 in OCI, net of taxes	$ 1,395	$ (996)	$ 3,944	$ (923)
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income, net of taxes	(40)	(103)	(156)	(148)
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 in Income on Derivatives	2,206	(1,801)	7,292	(378)
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	1,458	1,299	2,507	2,416
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	10	14
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	228	(1,526)	3,615	(1,886)
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	517	(1,586)	1,165	(931)
Not Designated as Hedging Instruments | Other contracts | Other income
Derivative Instruments and Hedging Activities Disclosures
Amount of Gain (Loss) Recognized in Income on Derivatives	$ (2)	$ 5	$ (5)	$ 9