Derivative Financial Instruments (Counterparty Credit Risk Narrative) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Maximum Length of Time Hedged in Cash Flow Hedge	4 years
Derivative instrument asset, Amount Offset	$ 33,730	$ 8,100
Derivative, Collateral, Right to Reclaim Cash	357,600
Credit Derivative, Maximum Exposure, Undiscounted	352,100
Valuation, Market Approach [Member]
Derivative [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	40,200
CME [Member]
Derivative [Line Items]
Derivative instrument asset, Amount Offset	85,400
Derivative, Collateral, Right to Reclaim Cash	$ 300,300