Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands		Dec. 31, 2017		Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		$ 3,531,427	[1]	$ 104,281
Loans held for sale		35,258		409,152
Mortgage servicing rights		2,729		228,099
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		3,531,427		104,281
Loans held for sale		35,258		409,152
Mortgage servicing rights		2,729		228,099
Derivative assets-other, netting adjustment	[2],[3]			(17,861)
Derivative liabilities, netting adjustment	[3]			16,588
Interest rate lock commitments				982
Derivative assets-other	[2]			1,579
Derivative liabilities				(7,140)
Fair Value, Measurements, Recurring | Mortgage-Related Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		2,618,746		7,326
Fair Value, Measurements, Recurring | Mortgage-Related Securities | GSE certificates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		2,068,842		7,326
Fair Value, Measurements, Recurring | Mortgage-Related Securities | GSE CMOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		549,904
Fair Value, Measurements, Recurring | Other Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		912,681		96,955
Fair Value, Measurements, Recurring | Other Securities | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		199,898
Fair Value, Measurements, Recurring | Other Securities | GSE debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		473,258
Fair Value, Measurements, Recurring | Other Securities | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		90,775
Fair Value, Measurements, Recurring | Other Securities | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		70,120		631
Fair Value, Measurements, Recurring | Other Securities | Capital trust notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		46,096		7,243
Fair Value, Measurements, Recurring | Other Securities | Preferred stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		15,434		71,984
Fair Value, Measurements, Recurring | Other Securities | Mutual Funds and Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		17,100		17,097
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		215,332		42,724
Derivative assets-other	[2]			2,611
Derivative liabilities				(6,009)
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		215,332		42,724
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Securities | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		199,898
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Securities | Preferred stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		15,434		42,724
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		3,316,095		61,557
Loans held for sale		35,258		409,152
Derivative assets-other	[2]			16,829
Derivative liabilities				(17,719)
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage-Related Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		2,618,746		7,326
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage-Related Securities | GSE certificates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		2,068,842		7,326
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage-Related Securities | GSE CMOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		549,904
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		697,349		54,231
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other Securities | GSE debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		473,258
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other Securities | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		90,775
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other Securities | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		70,120		631
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other Securities | Capital trust notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		46,096		7,243
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other Securities | Preferred stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale				29,260
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other Securities | Mutual Funds and Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		17,100		17,097
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage servicing rights		$ 2,729		228,099
Interest rate lock commitments				$ 982

[1] The amortized cost includes the non-credit portion of OTTI recorded in AOCL. At December 31, 2017, the non-credit portion of OTTI recorded in AOCL was $8.6 million (before taxes).

[2] Includes $1.9 million to purchase Treasury options.

[3] Includes cash collateral received from, and paid to, counterparties.