Derivative Financial Instruments (Counterparty Credit Risk Narrative) (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Maximum Length of Time Hedged in Cash Flow Hedge	4 years
Derivative instrument asset, Amount Offset	$ 36,739	$ 8,100
Derivative, Collateral, Right to Reclaim Cash	377,700
Credit Derivative, Maximum Exposure, Undiscounted	362,900
Derivative Credit Risk Valuation Adjustment, Derivative Assets (Liabilities)	5,500
Cash and Due from Banks [Member]
Derivative [Line Items]
Derivative, Collateral, Right to Reclaim Cash	36,900
Valuation, Market Approach [Member]
Derivative [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	40,700
CME [Member]
Derivative [Line Items]
Derivative instrument asset, Amount Offset	91,600
Derivative, Collateral, Right to Reclaim Cash	$ 316,100