Derivative Financial Instruments (Schedule fair value of derivative instruments) (Detail) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	$ 5,817,983,000	$ 6,198,556,000
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	401,164,000	146,037,000
Derivative Asset, Fair Value, Amount Offset Against Collateral	12,212,000	4,779,000
Asset Derivatives, Fair Value, Less: Cash collateral posted	33,730,000	8,100,000
Gross derivative instruments, before netting (1)	355,222,000	133,158,000
Liability Derivatives, Notional Amount	4,809,082,000	4,722,801,000
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	18,803,000	13,813,000
Derivative Liability, Fair Value, Amount Offset Against Collateral	12,212,000	4,779,000
Liability Derivatives, Fair Value, Less: Cash collateral posted	5,437,000	1,871,000
Derivative liability	1,154,000	7,163,000
CME [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value, Less: Cash collateral posted	85,400,000
Gross derivative instruments, before netting (1)	0
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	46,762,000	13,012,000
Derivative Asset, Fair Value, Amount Offset Against Collateral	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
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	45,910,000	11,855,000
Liability Derivatives, Notional Amount	75,000,000	300,000,000
Derivative Liability, Fair Value, Gross Liability	417,000	3,153,000
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	4,667,983,000	4,973,556,000
Asset Derivatives, Fair Value, Positions not subject to master netting agreement	355,254,000	134,182,000
Liability Derivatives, Notional Amount	4,734,082,000	4,422,801,000
Liability Derivatives, Fair Value, Positions not subject to master netting agreement	18,386,000	10,660,000
Not Designated as Hedging Instrument [Member] | Interest Rate Swap, CME [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	10,000,000.0	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	4,483,609,000	4,869,139,000
Derivative Asset, Fair Value, Gross Asset	352,782,000	133,455,000
Liability Derivatives, Notional Amount	4,475,948,000	4,090,522,000
Derivative Liability, Fair Value, Gross Liability	17,017,000	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	78,100,000
Not Designated as Hedging Instrument [Member] | Credit Risk Contract [Member] | RPA-In [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Notional Amount	208,400,000
Not Designated as Hedging Instrument [Member] | Mortgage Banking Derivatives [Member] | RPA-Out [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	79,265,000	27,873,000
Derivative Asset, Fair Value, Gross Asset	1,401,000	329,000
Not Designated as Hedging Instrument [Member] | Mortgage Banking Derivatives [Member] | RPA-In [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Notional Amount	5,000,000	57,000,000
Derivative Liability, Fair Value, Gross Liability	189,000	110,000
Not Designated as Hedging Instrument [Member] | Other Contract [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	105,109,000	76,544,000
Derivative Asset, Fair Value, Gross Asset	1,071,000	398,000
Liability Derivatives, Notional Amount	253,134,000	275,279,000
Derivative Liability, Fair Value, Gross Liability	1,180,000	$ 818,000
Interest Rate Lock Commitments [Member]
Derivatives, Fair Value [Line Items]
Other Commitment	$ 9,800,000