Derivative Financial Instruments (Schedule fair value of derivative instruments) (Detail) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	$ 6,094,742,000	$ 4,859,561,000
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	201,343,000	46,278,000
Derivative Asset, Fair Value, Amount Offset Against Collateral	6,240,000	2,495,000
Asset Derivatives, Fair Value, Less: Cash collateral posted	13,299,000	4,936,000
Derivative Asset	181,804,000	38,847,000
Liability Derivatives, Notional Amount	4,251,935,000	3,801,586,000
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	10,060,000	39,010,000
Derivative Liability, Fair Value, Amount Offset Against Collateral	6,240,000	2,495,000
Liability Derivatives, Fair Value, Less: Cash collateral posted	2,506,000	0
Derivative liability	1,314,000	36,515,000
CME [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value, Less: Cash collateral posted	57,800,000
Derivative Asset	0
Interest Rate Floor [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	1,000,000,000.0
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	19,683,000	9,928,000
Derivative Asset, Fair Value, Amount Offset Against Collateral	19,539,000	7,431,000
Derivative Asset	144,000	2,497,000
Derivative Liability, Fair Value, Gross Liability	8,816,000	2,566,000
Derivative Liability, Fair Value, Amount Offset Against Collateral	8,746,000	2,495,000
Derivative liability	70,000	71,000
Designated as Hedging Instrument [Member] | CME [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value, Less: Cash collateral posted	13,300,000
Designated as Hedging Instrument [Member] | Interest rate derivatives [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	1,525,000,000	325,000,000
Derivative Asset, Fair Value, Gross Asset	19,209,000	3,050,000
Liability Derivatives, Notional Amount	0	0
Derivative Liability, Fair Value, Gross Liability	0	0
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	4,569,742,000	4,534,561,000
Asset Derivatives, Fair Value, Positions not subject to master netting agreement	182,134,000	43,228,000
Liability Derivatives, Notional Amount	4,251,935,000	3,801,586,000
Liability Derivatives, Fair Value, Positions not subject to master netting agreement	10,060,000	39,010,000
Not Designated as Hedging Instrument [Member] | Interest Rate Swap, CME [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	700,000,000	1,900,000,000
Liability Derivatives, Notional Amount	2,800,000,000	1,100,000,000
Not Designated as Hedging Instrument [Member] | Interest rate derivatives [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	4,401,353,000	4,435,530,000
Derivative Asset, Fair Value, Gross Asset	180,852,000	42,205,000
Liability Derivatives, Notional Amount	4,026,716,000	3,643,985,000
Derivative Liability, Fair Value, Gross Liability	9,114,000	38,029,000
Not Designated as Hedging Instrument [Member] | Credit Risk Contract [Member] | RPA-Out [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	65,000,000.0	65,000,000.0
Not Designated as Hedging Instrument [Member] | Credit Risk Contract [Member] | RPA-In [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Notional Amount	139,500,000	96,300,000
Not Designated as Hedging Instrument [Member] | Mortgage Banking Derivatives [Member] | RPA-Out [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	61,367,000	13,599,000
Derivative Asset, Fair Value, Gross Asset	506,000	226,000
Not Designated as Hedging Instrument [Member] | Mortgage Banking Derivatives [Member] | RPA-In [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Notional Amount	74,000,000	17,000,000
Derivative Liability, Fair Value, Gross Liability	184,000	293,000
Not Designated as Hedging Instrument [Member] | Other Contract [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	107,022,000	85,432,000
Derivative Asset, Fair Value, Gross Asset	776,000	797,000
Liability Derivatives, Notional Amount	151,219,000	140,601,000
Derivative Liability, Fair Value, Gross Liability	762,000	$ 688,000
Loan Origination Commitments [Member]
Derivatives, Fair Value [Line Items]
Other Commitment	74,000,000.0
Interest Rate Lock Commitments [Member]
Derivatives, Fair Value [Line Items]
Other Commitment	$ 11,000,000.0