Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Statement of Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	$ 13,922	$ 12,219	$ 21,707
Interest Rate Swap Agreements [Member] | Fixed Rate Long-Term Borrowings [Member] | Derivatives Designated and Qualifying as Hedging Instruments [Member] | Fair Value Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives in fair value hedging relationships, Derivatives	(10,006)	(52,392)	(32,000)
Derivatives in fair value hedging relationships, Hedged item	10,969	51,628	30,906
Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	4,506	5,398	14,042
Foreign Exchange and Other Option and Futures Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	$ 9,416	$ 6,821	$ 7,665