Loans and Leases - Quality of Non-Covered Loans (Excluding PCI Loans and Leases) (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 7,018,522
Non-Covered Loans	42,235,977	$ 41,844,019
Multi-Family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Covered Loans	31,271,073	31,158,672
Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Covered Loans	7,034,720	7,081,910
One-to-four family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Covered Loans	352,301	380,361
Acquisition, development, and construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Covered Loans	130,675	200,596
Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	566,000
Non-Covered Loans	3,437,694	3,014,378
Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-Covered Loans	9,514	8,102
Non-Covered Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	52,110	64,963
Non- Accrual	49,282	61,243
Current	42,183,867	41,779,056
Non-Covered Loans | Financing Receivable, 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,828	3,720
Non-Covered Loans | Multi-Family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,921	6,538
Non- Accrual	4,242	5,407
Current	31,264,152	31,152,134
Non-Covered Loans | Multi-Family | Financing Receivable, 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,679	1,131
Non-Covered Loans | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	16,198	17,375
Non- Accrual	16,101	14,830
Current		7,064,535
Non-Covered Loans | Commercial Real Estate | Financing Receivable, 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	97	2,545
Non-Covered Loans | One-to-four family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,721	1,730
Non- Accrual	1,721	1,730
Current	350,580	378,631
Non-Covered Loans | Acquisition, development, and construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	130,675	200,596
Non-Covered Loans | Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	27,098	39,024
Non- Accrual	27,060	39,024
Current	3,410,596	2,975,354
Non-Covered Loans | Commercial and Industrial | Financing Receivable, 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	38	0
Non-Covered Loans | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	172	296
Non- Accrual	158	252
Current	9,342	7,806
Non-Covered Loans | Other | Financing Receivable, 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 14	$ 44