Loans and Leases - Quality of Loans Held for Investment (Details) - USD ($) $ in Thousands		Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans Receivable		$ 42,767,551	$ 41,844,019
Multi-Family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans Receivable		32,100,281	31,158,672
Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans Receivable		6,884,667	7,081,910
One-to-Four Family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans Receivable		274,095	380,361
Acquisition, Development, and Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans Receivable		86,007	200,596
Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual Loans		5,700
Total Loans Receivable	[1],[2]	3,416,040	3,014,378
Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans Receivable		6,461	8,102
Non-Covered Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		50,480	64,963
Non- Accrual Loans		45,351	61,243
Current Loans		42,717,071	41,779,056
Total Loans Receivable		42,767,551	41,844,019
Non-Covered Loans | Financing Receivable, 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		5,129	3,720
Non-Covered Loans | Multi-Family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		4,446	6,538
Non- Accrual Loans		4,068	5,407
Current Loans		32,095,835	31,152,134
Total Loans Receivable		32,100,281	31,158,672
Non-Covered Loans | Multi-Family | Financing Receivable, 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		378	1,131
Non-Covered Loans | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		15,290	17,375
Non- Accrual Loans		12,673	14,830
Current Loans		6,869,377	7,064,535
Total Loans Receivable		6,884,667	7,081,910
Non-Covered Loans | Commercial Real Estate | Financing Receivable, 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		2,617	2,545
Non-Covered Loans | One-to-Four Family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		3,784	1,730
Non- Accrual Loans		1,706	1,730
Current Loans		270,311	378,631
Total Loans Receivable		274,095	380,361
Non-Covered Loans | One-to-Four Family | Financing Receivable, 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		2,078
Non-Covered Loans | Acquisition, Development, and Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current Loans		86,007	200,596
Total Loans Receivable		86,007	200,596
Non-Covered Loans | Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		26,902	39,024
Non- Accrual Loans		26,902	39,024
Current Loans		3,389,138	2,975,354
Total Loans Receivable		3,416,040	3,014,378
Non-Covered Loans | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		58	296
Non- Accrual Loans		2	252
Current Loans		6,403	7,806
Total Loans Receivable		6,461	8,102
Non-Covered Loans | Other | Financing Receivable, 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans		$ 56	$ 44

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

[2] 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.