Loans Receivable and Allowance for Credit Losses (Credit Risk Ratings and/or Vintage Years for Loans Held-for-Investment by Portfolio Segment) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 9,787,213
2019	6,816,315
2018	5,125,324
2017	3,167,275
2016	1,547,971
Prior	3,277,221
Revolving Loans Amortized Cost Basis	8,390,152
Revolving Loans Converted to Term Loans Amortized Cost Basis	279,484
Loans held-for-investment	38,390,955	$ 34,778,539
Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		34,555,668
PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		222,871
Federal Housing Administration Loan
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Recorded Investment, 90 Days Past Due And Still Accruing, Classified As Pass	747	686
Pass \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		33,582,886
Pass \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		211,635
Criticized (accrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		853,249
Criticized (accrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		10,939
Criticized (nonaccrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		119,533
Criticized (nonaccrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		297
Commercial Lending
Financing Receivable, Credit Quality Indicator [Line Items]
2020	7,390,682
2019	5,000,429
2018	3,619,488
2017	2,129,478
2016	1,013,095
Prior	2,244,535
Revolving Loans Amortized Cost Basis	6,993,769
Revolving Loans Converted to Term Loans Amortized Cost Basis	48,551
Loans held-for-investment	28,440,027	25,914,252
Commercial Lending \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		25,777,039
Commercial Lending \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		137,213
Commercial Lending \| Pass \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		24,836,765
Commercial Lending \| Pass \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		126,269
Commercial Lending \| Criticized (accrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		848,179
Commercial Lending \| Criticized (accrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		10,939
Commercial Lending \| Criticized (nonaccrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		92,095
Commercial Lending \| Criticized (nonaccrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		5
Commercial Lending \| C&I
Financing Receivable, Credit Quality Indicator [Line Items]
2020	4,034,455
2019	1,577,608
2018	562,750
2017	283,807
2016	75,933
Prior	253,079
Revolving Loans Amortized Cost Basis	6,814,607
Revolving Loans Converted to Term Loans Amortized Cost Basis	29,487
Loans held-for-investment	13,631,726	12,150,931
Commercial Lending \| C&I \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		12,149,121
Commercial Lending \| C&I \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		1,810
Commercial Lending \| C&I \| Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,912,147
2019	1,477,740
2018	483,725
2017	245,594
2016	69,482
Prior	245,615
Revolving Loans Amortized Cost Basis	6,431,003
Revolving Loans Converted to Term Loans Amortized Cost Basis	29,487
Loans held-for-investment	12,894,793
Commercial Lending \| C&I \| Pass \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		11,423,094
Commercial Lending \| C&I \| Pass \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		1,810
Commercial Lending \| C&I \| Criticized (accrual)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	120,183
2019	74,601
2018	56,785
2017	19,426
2016	1,487
Prior	5,872
Revolving Loans Amortized Cost Basis	324,640
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Loans held-for-investment	602,994
Commercial Lending \| C&I \| Criticized (accrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		651,192
Commercial Lending \| C&I \| Criticized (accrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		0
Commercial Lending \| C&I \| Criticized (nonaccrual)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,125
2019	25,267
2018	22,240
2017	18,787
2016	4,964
Prior	1,592
Revolving Loans Amortized Cost Basis	58,964
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Loans held-for-investment	133,939
Commercial Lending \| C&I \| Criticized (nonaccrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		74,835
Commercial Lending \| C&I \| Criticized (nonaccrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		0
Commercial Lending \| CRE
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,344,108
2019	2,465,790
2018	2,396,262
2017	1,427,625
2016	734,788
Prior	1,613,707
Revolving Loans Amortized Cost Basis	173,267
Revolving Loans Converted to Term Loans Amortized Cost Basis	19,064
Loans held-for-investment	11,174,611	10,278,448
Commercial Lending \| CRE \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		10,165,247
Commercial Lending \| CRE \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		113,201
Commercial Lending \| CRE \| Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,296,649
2019	2,402,136
2018	2,310,748
2017	1,328,251
2016	732,694
Prior	1,529,681
Revolving Loans Amortized Cost Basis	173,267
Revolving Loans Converted to Term Loans Amortized Cost Basis	19,064
Loans held-for-investment	10,792,490
Commercial Lending \| CRE \| Pass \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		10,003,749
Commercial Lending \| CRE \| Pass \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		102,257
Commercial Lending \| CRE \| Criticized (accrual)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	47,459
2019	63,654
2018	43,447
2017	98,259
2016	2,094
Prior	80,662
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Loans held-for-investment	335,575
Commercial Lending \| CRE \| Criticized (accrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		145,057
Commercial Lending \| CRE \| Criticized (accrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		10,939
Commercial Lending \| CRE \| Criticized (nonaccrual)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	42,067
2017	1,115
2016	0
Prior	3,364
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Loans held-for-investment	46,546
Commercial Lending \| CRE \| Criticized (nonaccrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		16,441
Commercial Lending \| CRE \| Criticized (nonaccrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		5
Commercial Lending \| Real estate loan \| Multifamily
Financing Receivable, Credit Quality Indicator [Line Items]
2020	783,671
2019	784,324
2018	503,764
2017	418,046
2016	181,477
Prior	356,821
Revolving Loans Amortized Cost Basis	5,895
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Loans held-for-investment	3,033,998	2,856,374
Commercial Lending \| Real estate loan \| Multifamily \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		2,834,212
Commercial Lending \| Real estate loan \| Multifamily \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		22,162
Commercial Lending \| Real estate loan \| Multifamily \| Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	783,671
2019	783,589
2018	479,959
2017	411,945
2016	181,213
Prior	348,751
Revolving Loans Amortized Cost Basis	5,895
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Loans held-for-investment	2,995,023
Commercial Lending \| Real estate loan \| Multifamily \| Pass \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		2,806,475
Commercial Lending \| Real estate loan \| Multifamily \| Pass \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		22,162
Commercial Lending \| Real estate loan \| Multifamily \| Criticized (accrual)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	735
2018	22,330
2017	6,101
2016	264
Prior	5,877
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Loans held-for-investment	35,307
Commercial Lending \| Real estate loan \| Multifamily \| Criticized (accrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		26,918
Commercial Lending \| Real estate loan \| Multifamily \| Criticized (accrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		0
Commercial Lending \| Real estate loan \| Multifamily \| Criticized (nonaccrual)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	1,475
2017	0
2016	0
Prior	2,193
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Loans held-for-investment	3,668
Commercial Lending \| Real estate loan \| Multifamily \| Criticized (nonaccrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		819
Commercial Lending \| Real estate loan \| Multifamily \| Criticized (nonaccrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		0
Commercial Lending \| Construction and land
Financing Receivable, Credit Quality Indicator [Line Items]
2020	228,448
2019	172,707
2018	156,712
2017	0
2016	20,897
Prior	20,928
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Loans held-for-investment	599,692	628,499
Commercial Lending \| Construction and land \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		628,459
Commercial Lending \| Construction and land \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		40
Commercial Lending \| Construction and land \| Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	224,924
2019	172,707
2018	156,712
2017	0
2016	20,897
Prior	1,028
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Loans held-for-investment	576,268
Commercial Lending \| Construction and land \| Pass \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		603,447
Commercial Lending \| Construction and land \| Pass \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		40
Commercial Lending \| Construction and land \| Criticized (accrual)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,524
2019	0
2018	0
2017	0
2016	0
Prior	19,900
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Loans held-for-investment	23,424
Commercial Lending \| Construction and land \| Criticized (accrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		25,012
Commercial Lending \| Construction and land \| Criticized (accrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		0
Commercial Lending \| Construction and land \| Criticized (nonaccrual)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Loans held-for-investment	0
Commercial Lending \| Construction and land \| Criticized (nonaccrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		0
Commercial Lending \| Construction and land \| Criticized (nonaccrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		0
Commercial Lending \| Total CRE
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,356,227
2019	3,422,821
2018	3,056,738
2017	1,845,671
2016	937,162
Prior	1,991,456
Revolving Loans Amortized Cost Basis	179,162
Revolving Loans Converted to Term Loans Amortized Cost Basis	19,064
Loans held-for-investment	14,808,301	13,763,321
Commercial Lending \| Total CRE \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		13,627,918
Commercial Lending \| Total CRE \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		135,403
Commercial Lending \| Total CRE \| Pass \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		13,413,671
Commercial Lending \| Total CRE \| Pass \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		124,459
Commercial Lending \| Total CRE \| Criticized (accrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		196,987
Commercial Lending \| Total CRE \| Criticized (accrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		10,939
Commercial Lending \| Total CRE \| Criticized (nonaccrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		17,260
Commercial Lending \| Total CRE \| Criticized (nonaccrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		5
Consumer Lending
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,396,531
2019	1,815,886
2018	1,505,836
2017	1,037,797
2016	534,876
Prior	1,032,686
Revolving Loans Amortized Cost Basis	1,396,383
Revolving Loans Converted to Term Loans Amortized Cost Basis	230,933
Loans held-for-investment	9,950,928	8,864,287
Consumer Lending \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		8,778,629
Consumer Lending \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		85,658
Consumer Lending \| Pass \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		8,746,121
Consumer Lending \| Pass \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		85,366
Consumer Lending \| Criticized (accrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		5,070
Consumer Lending \| Criticized (accrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		0
Consumer Lending \| Criticized (nonaccrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		27,438
Consumer Lending \| Criticized (nonaccrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		292
Consumer Lending \| Real estate loan \| Single-family
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,385,853
2019	1,814,855
2018	1,502,472
2017	1,023,496
2016	525,283
Prior	933,994
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Loans held-for-investment	8,185,953	7,108,590
Consumer Lending \| Real estate loan \| Single-family \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		7,028,979
Consumer Lending \| Real estate loan \| Single-family \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		79,611
Consumer Lending \| Real estate loan \| Single-family \| Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,385,853
2019	1,813,200
2018	1,501,660
2017	1,021,707
2016	523,170
Prior	921,714
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Loans held-for-investment	8,167,304
Consumer Lending \| Real estate loan \| Single-family \| Pass \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		7,012,522
Consumer Lending \| Real estate loan \| Single-family \| Pass \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		79,517
Consumer Lending \| Real estate loan \| Single-family \| Criticized (accrual)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	1,429
2018	0
2017	0
2016	119
Prior	1,034
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Loans held-for-investment	2,582
Consumer Lending \| Real estate loan \| Single-family \| Criticized (accrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		2,278
Consumer Lending \| Real estate loan \| Single-family \| Criticized (accrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		0
Consumer Lending \| Real estate loan \| Single-family \| Criticized (nonaccrual)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	226
2018	812
2017	1,789
2016	1,994
Prior	11,246
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Loans held-for-investment	16,067
Consumer Lending \| Real estate loan \| Single-family \| Criticized (nonaccrual) \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		14,179
Consumer Lending \| Real estate loan \| Single-family \| Criticized (nonaccrual) \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		94
Consumer Lending \| HELOCs
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,131
2019	1,031
2018	3,364
2017	9,980
2016	9,593
Prior	15,437
Revolving Loans Amortized Cost Basis	1,330,247
Revolving Loans Converted to Term Loans Amortized Cost Basis	230,933
Loans held-for-investment	1,601,716	1,472,783
Consumer Lending \| HELOCs \| Non-PCI impaired loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		1,466,736
Consumer Lending \| HELOCs \| PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans held-for-investment		6,047
Consumer Lending \| HELOCs \| Pass

Loans Receivable and Allowance for Credit Losses (Credit Risk Ratings and/or Vintage Years for Loans Held-for-Investment by Portfolio Segment) (Details) - USD ($)
$ in Thousands