Derivative Financial Instruments (Offsetting Derivatives) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Derivative instrument asset, Amount Offset, Total		$ (4,779)	$ (2,495)
Derivative instrument asset, Amount Offset		8,100	4,936
Derivative asset		133,158	38,847
Derivative Liability, Fair Value, Amount Offset Against Collateral		4,779	2,495
Derivative Liability, Collateral, Right to Reclaim Cash, Offset		(1,871)	0
Derivative liability		7,163	36,515
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	$ (299)		0
Derivative Asset, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	(432)		(2,497)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(329)		(756)
Derivative Liability, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	(389)		(827)
Hedge Accounting Positions [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	13,012		9,928
Derivative instrument asset, Amount Offset, Total	(12,879)		(7,431)
Derivative asset	133		2,497
Derivative Liability, Fair Value, Gross Liability	6,710		2,566
Derivative Liability, Fair Value, Amount Offset Against Collateral	6,650		2,495
Derivative liability	$ 60		71
Interest Rate Derivatives [Member] | Hedge Accounting Positions [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset		11,855	3,050
Derivative Liability, Fair Value, Gross Liability		$ 3,153	$ 0