Derivative Financial Instruments (Schedule fair value of derivative instruments) (Detail) - USD ($)		Jun. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Derivative instrument assets, Gross Amount		$ 6,578,000	$ 9,928,000
Asset Derivatives, Fair Value, Less: Cash collateral posted		40,400,000
Derivative Asset		2,706,000	2,497,000
Liability Derivatives, Fair Value, Gross Liability		10,615,000	2,566,000
Derivative liability		2,944,000	71,000
CME [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset		0
Subject to and not subject to Master Netting Agreements [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts		5,433,863,000	4,859,561,000
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement		142,433,000	46,278,000
Asset Derivatives, Fair Value, Less: Legally enforceable master netting agreements		2,367,000	2,495,000
Asset Derivatives, Fair Value, Less: Cash collateral posted		1,505,000	4,936,000
Derivative Asset		138,561,000	38,847,000
Liability Derivatives, Notional Amount		4,325,924,000	3,801,586,000
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		14,045,000	39,010,000
Liability Derivatives, Fair Value, Less: Legally enforceable master netting agreements		2,367,000	2,495,000
Liability Derivatives, Fair Value, Less: Cash collateral posted		5,304,000	0
Derivative liability		6,374,000	36,515,000
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative instrument assets, Gross Amount		4,515,000	3,050,000
Asset Derivatives, Fair Value, Less: Legally enforceable master netting agreements		970,000	88,000
Asset Derivatives, Fair Value, Less: Cash collateral posted		1,505,000	567,000
Derivative Asset		2,040,000	2,395,000
Liability Derivatives, Fair Value, Gross Liability		0	0
Liability Derivatives, Fair Value, Less: Legally enforceable master netting agreements		0	0
Liability Derivatives, Fair Value, Less: Cash collateral posted		0	0
Derivative liability		0	0
Designated as Hedging Instrument [Member] | Derivatives Subject to Master Netting Arrangement or Similar Arrangement [Member] | Interest rate derivatives [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	[1]	825,000,000	325,000,000
Derivative instrument assets, Gross Amount	[1]	4,515,000	3,050,000
Liability Derivatives, Notional Amount	[1]	0	0
Liability Derivatives, Fair Value, Gross Liability	[1]	0	0
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative instrument assets, Gross Amount		2,063,000	6,878,000
Asset Derivatives, Fair Value, Less: Legally enforceable master netting agreements		1,397,000	2,407,000
Asset Derivatives, Fair Value, Less: Cash collateral posted		0	4,369,000
Derivative Asset		666,000	102,000
Liability Derivatives, Fair Value, Gross Liability		10,615,000	2,566,000
Liability Derivatives, Fair Value, Less: Legally enforceable master netting agreements		2,367,000	2,495,000
Liability Derivatives, Fair Value, Less: Cash collateral posted		5,304,000	0
Derivative liability		2,944,000	71,000
Not Designated as Hedging Instrument [Member] | CME [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	[1]	900,000,000	1,900,000,000
Liability Derivatives, Notional Amount	[1]	2,600,000,000	1,100,000,000
Not Designated as Hedging Instrument [Member] | Derivatives Subject to Master Netting Arrangement or Similar Arrangement [Member] | Interest rate derivatives [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	[1]	1,398,175,000	2,767,518,000
Derivative instrument assets, Gross Amount	[1]	1,578,000	6,570,000
Liability Derivatives, Notional Amount	[1]	2,905,312,000	1,276,109,000
Liability Derivatives, Fair Value, Gross Liability	[1]	9,617,000	2,012,000
Not Designated as Hedging Instrument [Member] | Derivatives Subject to Master Netting Arrangement or Similar Arrangement [Member] | Mortgage Banking Derivatives [Member] | RPA-Out [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts		42,284,000	13,599,000
Derivative instrument assets, Gross Amount		374,000	226,000
Not Designated as Hedging Instrument [Member] | Derivatives Subject to Master Netting Arrangement or Similar Arrangement [Member] | Mortgage Banking Derivatives [Member] | RPA-In [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Notional Amount		46,073,000	17,000,000
Liability Derivatives, Fair Value, Gross Liability		399,000	293,000
Not Designated as Hedging Instrument [Member] | Derivatives Subject to Master Netting Arrangement or Similar Arrangement [Member] | Other Contract [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts	[1]	13,124,000	11,952,000
Derivative instrument assets, Gross Amount	[1]	111,000	308,000
Liability Derivatives, Notional Amount	[1]	53,318,000	43,097,000
Liability Derivatives, Fair Value, Gross Liability	[1]	599,000	553,000
Not Designated as Hedging Instrument [Member] | Derivatives Not Subject to Master Netting Arrangement or Similar Arrangement [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts		4,608,863,000	4,534,561,000
Asset Derivatives, Fair Value, Positions not subject to master netting agreement		137,918,000	43,228,000
Liability Derivatives, Notional Amount		4,325,924,000	3,801,586,000
Liability Derivatives, Fair Value, Positions not subject to master netting agreement		14,045,000	39,010,000
Not Designated as Hedging Instrument [Member] | Derivatives Not Subject to Master Netting Arrangement or Similar Arrangement [Member] | Interest rate derivatives [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts		3,084,348,000	1,668,012,000
Asset Derivatives, Fair Value, Positions not subject to master netting agreement		135,374,000	35,635,000
Liability Derivatives, Notional Amount		1,218,947,000	2,367,876,000
Liability Derivatives, Fair Value, Positions not subject to master netting agreement		3,250,000	36,017,000
Not Designated as Hedging Instrument [Member] | Derivatives Not Subject to Master Netting Arrangement or Similar Arrangement [Member] | Credit Risk Contract [Member] | RPA-Out [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts		64,382,000	64,974,000
Asset Derivatives, Fair Value, Positions not subject to master netting agreement		88,000	39,000
Not Designated as Hedging Instrument [Member] | Derivatives Not Subject to Master Netting Arrangement or Similar Arrangement [Member] | Credit Risk Contract [Member] | RPA-In [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Notional Amount		101,565,000	96,296,000
Liability Derivatives, Fair Value, Positions not subject to master netting agreement		137,000	81,000
Not Designated as Hedging Instrument [Member] | Derivatives Not Subject to Master Netting Arrangement or Similar Arrangement [Member] | Other Contract [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional Amounts		6,550,000	8,506,000
Asset Derivatives, Fair Value, Positions not subject to master netting agreement		393,000	450,000
Liability Derivatives, Notional Amount		709,000	1,208,000
Liability Derivatives, Fair Value, Positions not subject to master netting agreement		43,000	$ 54,000
Loan Origination Commitments [Member]
Derivatives, Fair Value [Line Items]
Other Commitment		45,000,000.0
Interest Rate Lock Commitments [Member]
Derivatives, Fair Value [Line Items]
Other Commitment		$ 12,300,000

[1] o report derivative positions subject to a legally enforceable master netting agreement on a net basis, net of cash collateral. Refer to the Offsetting Derivatives section of this footnote for additional information.