Derivative Financial Instruments (Offsetting Derivatives) (Detail) - USD ($)	Jun. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	$ 4,724,000	$ 7,522,000
Derivative instrument asset, Amount Offset	30,234,000	33,043,000
Gross derivative instruments, before netting (1)	191,276,000	292,291,000
Derivative Liability, Fair Value, Amount Offset Against Collateral	4,724,000	7,522,000
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	2,996,000	4,485,000
Derivative liability	8,572,000	347,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	134,000	785,000
Derivative Asset, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	134,000	785,000
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	1,915,000	1,247,000
Derivative Liability, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	1,915,000	1,247,000
Hedge Accounting Positions [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	34,958,000	40,565,000
Derivative Asset, Fair Value, Amount Offset Against Collateral	34,958,000	40,565,000
Gross derivative instruments, before netting (1)	0	0
Derivative Liability, Fair Value, Gross Liability	7,720,000	12,007,000
Derivative Liability, Fair Value, Amount Offset Against Collateral	7,720,000	12,007,000
Derivative liability	0	0
CME [Member]
Derivative [Line Items]
Derivative instrument asset, Amount Offset	72,700,000
Gross derivative instruments, before netting (1)	0
Interest Rate Derivatives [Member] | Hedge Accounting Positions [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	29,179,000	39,641,000
Derivative Liability, Fair Value, Gross Liability	$ 14,000	$ 103,000