Derivative Financial Instruments (Schedule fair value of derivative instruments) (Detail) - USD ($)	Jun. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	$ 5,909,498,000	$ 6,198,556,000
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	414,052,000	146,037,000
Derivative Asset, Fair Value, Amount Offset Against Collateral	12,318,000	4,779,000
Asset Derivatives, Fair Value, Less: Cash collateral posted	36,739,000	8,100,000
Gross derivative instruments, before netting (1)	364,995,000	133,158,000
Liability Derivatives, Notional Amount	4,905,312,000	4,722,801,000
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	19,538,000	13,813,000
Derivative Liability, Fair Value, Amount Offset Against Collateral	12,318,000	4,779,000
Liability Derivatives, Fair Value, Less: Cash collateral posted	6,313,000	1,871,000
Derivative liability	907,000	7,163,000
CME [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value, Less: Cash collateral posted	91,600,000
Gross derivative instruments, before netting (1)	0
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	49,104,000	13,012,000
Derivative Asset, Fair Value, Amount Offset Against Collateral	49,057,000	12,879,000
Gross derivative instruments, before netting (1)	47,000	133,000
Derivative Liability, Fair Value, Gross Liability	18,691,000	6,710,000
Derivative Liability, Fair Value, Amount Offset Against Collateral	18,631,000	6,650,000
Derivative liability	60,000	60,000
Designated as Hedging Instrument [Member] | Interest rate derivatives [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	1,150,000,000	1,225,000,000
Derivative Asset, Fair Value, Gross Asset	48,793,000	11,855,000
Liability Derivatives, Notional Amount	75,000,000	300,000,000
Derivative Liability, Fair Value, Gross Liability	331,000	3,153,000
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	4,759,498,000	4,973,556,000
Asset Derivatives, Fair Value, Positions not subject to master netting agreement	365,259,000	134,182,000
Liability Derivatives, Notional Amount	4,830,312,000	4,422,801,000
Liability Derivatives, Fair Value, Positions not subject to master netting agreement	19,207,000	10,660,000
Not Designated as Hedging Instrument [Member] | Interest Rate Swap, CME [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	3,500,000	1,100,000,000
Liability Derivatives, Notional Amount	3,500,000,000	2,600,000,000
Not Designated as Hedging Instrument [Member] | Interest rate derivatives [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	4,565,049,000	4,869,139,000
Derivative Asset, Fair Value, Gross Asset	363,143,000	133,455,000
Liability Derivatives, Notional Amount	4,517,068,000	4,090,522,000
Derivative Liability, Fair Value, Gross Liability	17,874,000	9,732,000
Not Designated as Hedging Instrument [Member] | Credit Risk Contract [Member] | RPA-Out [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	92,700,000	65,700,000
Not Designated as Hedging Instrument [Member] | Credit Risk Contract [Member] | RPA-In [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Notional Amount	270,000,000.0	223,400,000
Not Designated as Hedging Instrument [Member] | Mortgage Banking Derivatives [Member] | RPA-Out [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	94,812,000	27,873,000
Derivative Asset, Fair Value, Gross Asset	1,846,000	329,000
Not Designated as Hedging Instrument [Member] | Mortgage Banking Derivatives [Member] | RPA-In [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Notional Amount	224,000	57,000,000
Derivative Liability, Fair Value, Gross Liability	1,000	110,000
Not Designated as Hedging Instrument [Member] | Other Contract [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	99,637,000	76,544,000
Derivative Asset, Fair Value, Gross Asset	270,000	398,000
Liability Derivatives, Notional Amount	313,020,000	275,279,000
Derivative Liability, Fair Value, Gross Liability	1,332,000	$ 818,000
Interest Rate Lock Commitments [Member]
Derivatives, Fair Value [Line Items]
Other Commitment	$ 8,100,000