Loans and Leases - Composition of Loan and Lease Portfolio (Details) - USD ($) $ in Thousands		Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 42,767,551	$ 41,844,019
Non-Covered Loans, Percentage		100.00%	100.00%
Net deferred loan origination costs		$ 61,668	$ 50,136
Allowance for loan and lease losses		(188,307)	(147,638)	$ (149,433)	$ (159,820)
Total loans and leases held for investment, net		42,640,912	41,746,517
Loans held for sale	[1]	117,272
Total loans and leases, net		42,758,184	41,746,517
Multi-Family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 32,100,281	$ 31,158,672
Non-Covered Loans, Percentage		75.06%	74.46%
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 6,884,667	$ 7,081,910
Non-Covered Loans, Percentage		16.10%	16.93%
One-to-Four Family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 274,095	$ 380,361
Non-Covered Loans, Percentage		0.64%	0.91%
Acquisition, Development, and Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 86,007	$ 200,596
Non-Covered Loans, Percentage		0.20%	0.48%
Mortgage Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans	[2]	$ 39,345,050	$ 38,821,539
Non-Covered Loans, Percentage	[2]	92.00%	92.78%
Allowance for loan and lease losses		$ (170,752)	$ (122,695)	$ (122,967)	$ (130,983)
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans	[3],[4]	$ 3,416,040	$ 3,014,378
Non-Covered Loans, Percentage	[4]	7.99%	7.20%
Commercial and Industrial | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 1,644,872	$ 1,742,380
Non-Covered Loans, Percentage		3.85%	4.16%
Lease Financing, Unearned Income
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 1,771,168	$ 1,271,998
Non-Covered Loans, Percentage		4.14%	3.04%
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 6,461	$ 8,102
Non-Covered Loans, Percentage		0.01%	0.02%
Total Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 3,422,501	$ 3,022,480
Total Other Loans | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans	[2]	$ 3,422,501	$ 3,022,480
Non-Covered Loans, Percentage	[2]	8.00%	7.22%

[1] Includes deferred loan origination fees of $1.7 million.

[2] Excludes accrued interest receivable of $217.8 million and $116.9 million at September 30, 2020 and December 31, 2019, respectively, which is included in other assets in the Consolidated Statements of Condition.

[3] Includes lease financing receivables, all of which were classified as Pass

[4] Includes specialty finance loans and leases of $3.1 billion and $2.6 billion, respectively, at September 30, 2020 and December 31, 2019, and other C&I loans of $394.3 million and $420.1 million, respectively, at September 30, 2020 and December 31, 2019.