Securities - Summary of Portfolio of Securities Available for Sale (Details) - USD ($) $ in Thousands		Sep. 30, 2020		Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 5,163,064	[1]	$ 5,841,796
Gross Unrealized Gain		136,449	[1]	77,498
Gross Unrealized Loss		34,321	[1]	33,407
Fair Value		5,265,192	[1]	5,885,887
Asset-backed Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		541,390	[2]	384,108
Gross Unrealized Gain	[2]	850
Gross Unrealized Loss		9,987	[2]	10,854
Fair Value		532,253	[2]	373,254
Mutual Funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		15,815
Gross Unrealized Gain		342
Fair Value		16,157
Mutual Funds and Common Stock
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost				16,871
Gross Unrealized Gain				718
Gross Unrealized Loss				173
Fair Value				17,416
Mortgage-related Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,544,414		3,313,757
Gross Unrealized Gain		108,690		47,282
Gross Unrealized Loss		108		7,304
Fair Value		2,652,996		3,353,735
Mortgage-related Securities | GSE Certificates
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,160,210		1,530,317
Gross Unrealized Gain		58,146		26,069
Gross Unrealized Loss		25		3,763
Fair Value		1,218,331		1,552,623
Mortgage-related Securities | GSE CMOs
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,384,204		1,783,440
Gross Unrealized Gain		50,544		21,213
Gross Unrealized Loss		83		3,541
Fair Value		1,434,665		1,801,112
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,587,543		2,495,876
Gross Unrealized Gain		27,417		29,376
Gross Unrealized Loss		34,212		25,930
Fair Value		2,580,748		2,499,322
Debt Securities | U.S. Treasury Obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		61,986		41,820
Gross Unrealized Gain		1		19
Gross Unrealized Loss		3
Fair Value		61,984		41,839
Debt Securities | GSE Debentures
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		991,865		1,093,845
Gross Unrealized Gain		5,739		5,707
Gross Unrealized Loss		3,639		5,312
Fair Value		993,965		1,094,240
Debt Securities | Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		26,304		26,808
Gross Unrealized Gain		667		559
Gross Unrealized Loss		114		475
Fair Value		26,857		26,892
Debt Securities | Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		870,610		854,195
Gross Unrealized Gain		14,949		15,970
Gross Unrealized Loss		8,761		2,983
Fair Value		876,798		867,182
Debt Securities | Capital Trust Notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		95,388		95,100
Gross Unrealized Gain		5,211		7,121
Gross Unrealized Loss		11,708		6,306
Fair Value		88,891		95,915
Mortgage Backed Securities And Other Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		5,131,957		5,809,633
Gross Unrealized Gain		136,107		76,658
Gross Unrealized Loss		34,320		33,234
Fair Value		5,233,744		5,853,057
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		31,107		32,163
Gross Unrealized Gain		342		840
Gross Unrealized Loss		1		173
Fair Value		31,448		32,830
Equity Securities | Preferred stock
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		15,292		15,292
Gross Unrealized Gain				122
Gross Unrealized Loss		1
Fair Value		$ 15,291		$ 15,414

[1] Excludes accrued interest receivable of $14.0 million included in other assets in the Consolidated Statements of Condition.

[2] The underlying assets of the asset-backed securities are substantially guaranteed by the U.S. Government.