Summary of Portfolio of Securities Available for Sale (Detail) - USD ($) $ in Thousands		Sep. 30, 2017		Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 2,948,919	[1]	$ 105,567
Gross Unrealized Gain		95,296	[1]	1,980
Gross Unrealized Loss		13,189	[1]	3,266
Fair Value		3,031,026	[1]	104,281
Mortgage-Related Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,434,796
Gross Unrealized Gain		76,950
Gross Unrealized Loss		1,217
Fair Value		2,510,529
Mortgage-Related Securities | GSE certificates
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,904,431	[2]	7,786
Gross Unrealized Gain	[2]	57,138
Gross Unrealized Loss		1,217	[2]	460
Fair Value		1,960,352	[2]	7,326
Mortgage-Related Securities | GSE CMOs
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	[3]	530,365
Gross Unrealized Gain	[3]	19,812
Fair Value	[3]	550,177
Other Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		514,123		97,781
Gross Unrealized Gain		18,346		1,980
Gross Unrealized Loss		11,972		2,806
Fair Value		520,497		96,955
Other Securities | Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		71,079		583
Gross Unrealized Gain		137		48
Gross Unrealized Loss		849
Fair Value		70,367		631
Other Securities | Capital trust notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		48,217		9,458
Gross Unrealized Gain		3,489		2
Gross Unrealized Loss		10,939		2,217
Fair Value		40,767		7,243
Other Securities | Preferred Stock (Par Value: $0.01):
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		15,293		70,866
Gross Unrealized Gain		46		1,446
Gross Unrealized Loss				328
Fair Value		15,339		71,984
Other Securities | Mutual Funds and Common Stock
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		16,874	[4]	16,874
Gross Unrealized Gain		488	[4]	484
Gross Unrealized Loss		184	[4]	261
Fair Value		17,178	[4]	$ 17,097
Other Securities | U.S. Treasury obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		199,838
Gross Unrealized Gain		37
Fair Value		199,875
Other Securities | GSE debentures
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		88,242
Gross Unrealized Gain		2,592
Fair Value		90,834
Other Securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		74,580
Gross Unrealized Gain		11,557
Fair Value		$ 86,137

[1] The amortized cost includes the non-credit portion of other-than-temporary impairment ("OTTI") recorded in accumulated other comprehensive loss ("AOCL"). At September 30, 2017, the non-credit portion of OTTI recorded in AOCL was $8.6 million (before taxes).

[2] Government-sponsored enterprise.

[3] Collateralized mortgage obligations.

[4] Primarily consists of mutual funds that are Community Reinvestment Act-qualified investments.