Derivative Financial Instruments - Information about Fair Values of Derivative Instruments in Consolidated Statement of Income (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	$ (321)	$ 2,399	$ 705	$ 6,185
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	(13,357)	(5,795)	(55,747)	(9,914)
Derivatives in fair value hedging relationships, Hedged item	13,884	5,011	56,254	9,023
Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	(2,686)	831	(4,291)	2,781
Foreign Exchange and Other Option and Futures Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as hedging instruments, Derivatives	$ 2,365	$ 1,568	$ 4,996	$ 3,404