Derivative Financial Instruments (Offsetting Derivatives) (Detail) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Derivative instrument asset, Amount Offset, Total	$ (12,212,000)	$ (4,779,000)
Derivative instrument asset, Amount Offset	33,730,000	8,100,000
Gross derivative instruments, before netting (1)	355,222,000	133,158,000
Derivative Liability, Fair Value, Amount Offset Against Collateral	12,212,000	4,779,000
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	(5,437,000)	(1,871,000)
Derivative liability	1,154,000	7,163,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(143,000)	(299,000)
Derivative Asset, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	(963,000)	(432,000)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0	(329,000)
Derivative Liability, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	(363,000)	(389,000)
Hedge Accounting Positions [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	46,762,000	13,012,000
Derivative instrument asset, Amount Offset, Total	(45,942,000)	(12,879,000)
Gross derivative instruments, before netting (1)	820,000	133,000
Derivative Liability, Fair Value, Gross Liability	18,012,000	6,710,000
Derivative Liability, Fair Value, Amount Offset Against Collateral	17,649,000	6,650,000
Derivative liability	363,000	60,000
CME [Member]
Derivative [Line Items]
Derivative instrument asset, Amount Offset	85,400,000
Gross derivative instruments, before netting (1)	0
Interest Rate Derivatives [Member] | Hedge Accounting Positions [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	45,910,000	11,855,000
Derivative Liability, Fair Value, Gross Liability	$ 417,000	$ 3,153,000