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	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	$ 3,250,204	$ 9,787,213
Fiscal Year before Current Fiscal Year	8,870,539	6,816,315
Two Years before Current Fiscal Year	6,356,839	5,125,324
Three Years before Current Fiscal Year	4,762,757	3,167,275
Four Years before Current Fiscal Year	2,944,099	1,547,971
Prior	4,549,488	3,277,221
Revolving Loans Amortized Cost Basis	8,541,074	8,390,152
Revolving Loans Converted to Term Loans Amortized Cost Basis	313,748	279,484
Total	39,588,748	38,390,955
Federal Housing Administration Loan
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Financing receivable, recorded investment, 90 days past due and still accruing, classified as pass	647	747
Commercial lending
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	2,579,695	7,390,682
Fiscal Year before Current Fiscal Year	6,434,251	5,000,429
Two Years before Current Fiscal Year	4,650,080	3,619,488
Three Years before Current Fiscal Year	3,372,479	2,129,478
Four Years before Current Fiscal Year	1,972,539	1,013,095
Prior	3,073,789	2,244,535
Revolving Loans Amortized Cost Basis	7,033,649	6,993,769
Revolving Loans Converted to Term Loans Amortized Cost Basis	53,431	48,551
Total	29,169,913	28,440,027
Commercial lending | Commercial and industrial (“C&I”)
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	1,716,561	4,034,455
Fiscal Year before Current Fiscal Year	3,190,361	1,577,608
Two Years before Current Fiscal Year	1,322,029	562,750
Three Years before Current Fiscal Year	436,496	283,807
Four Years before Current Fiscal Year	261,763	75,933
Prior	290,354	253,079
Revolving Loans Amortized Cost Basis	6,834,219	6,814,607
Revolving Loans Converted to Term Loans Amortized Cost Basis	29,327	29,487
Total	14,081,110	13,631,726
Commercial lending | Commercial and industrial (“C&I”) | Pass
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	1,661,034	3,912,147
Fiscal Year before Current Fiscal Year	3,043,315	1,477,740
Two Years before Current Fiscal Year	1,220,618	483,725
Three Years before Current Fiscal Year	385,813	245,594
Four Years before Current Fiscal Year	228,364	69,482
Prior	280,748	245,615
Revolving Loans Amortized Cost Basis	6,492,230	6,431,003
Revolving Loans Converted to Term Loans Amortized Cost Basis	29,327	29,487
Total	13,341,449	12,894,793
Commercial lending | Commercial and industrial (“C&I”) | Criticized (Accrual)
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	55,239	120,183
Fiscal Year before Current Fiscal Year	145,506	74,601
Two Years before Current Fiscal Year	83,989	56,785
Three Years before Current Fiscal Year	29,315	19,426
Four Years before Current Fiscal Year	18,541	1,487
Prior	6,809	5,872
Revolving Loans Amortized Cost Basis	274,726	324,640
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	614,125	602,994
Commercial lending | Commercial and industrial (“C&I”) | Criticized (Nonaccrual)
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	288	2,125
Fiscal Year before Current Fiscal Year	1,540	25,267
Two Years before Current Fiscal Year	17,422	22,240
Three Years before Current Fiscal Year	21,368	18,787
Four Years before Current Fiscal Year	14,858	4,964
Prior	2,797	1,592
Revolving Loans Amortized Cost Basis	67,263	58,964
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	125,536	133,939
Commercial lending | Commercial real estate (“CRE”)
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	693,541	2,344,108
Fiscal Year before Current Fiscal Year	2,337,933	2,465,790
Two Years before Current Fiscal Year	2,418,618	2,396,262
Three Years before Current Fiscal Year	2,320,640	1,427,625
Four Years before Current Fiscal Year	1,351,490	734,788
Prior	2,223,167	1,613,707
Revolving Loans Amortized Cost Basis	193,541	173,267
Revolving Loans Converted to Term Loans Amortized Cost Basis	24,104	19,064
Total	11,563,034	11,174,611
Commercial lending | Commercial real estate (“CRE”) | Pass
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	664,626	2,296,649
Fiscal Year before Current Fiscal Year	2,303,031	2,402,136
Two Years before Current Fiscal Year	2,354,998	2,310,748
Three Years before Current Fiscal Year	2,253,230	1,328,251
Four Years before Current Fiscal Year	1,284,384	732,694
Prior	2,128,975	1,529,681
Revolving Loans Amortized Cost Basis	193,541	173,267
Revolving Loans Converted to Term Loans Amortized Cost Basis	24,104	19,064
Total	11,206,889	10,792,490
Commercial lending | Commercial real estate (“CRE”) | Criticized (Accrual)
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	28,915	47,459
Fiscal Year before Current Fiscal Year	34,902	63,654
Two Years before Current Fiscal Year	63,620	43,447
Three Years before Current Fiscal Year	25,343	98,259
Four Years before Current Fiscal Year	61,238	2,094
Prior	91,993	80,662
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	306,011	335,575
Commercial lending | Commercial real estate (“CRE”) | Criticized (Nonaccrual)
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year before Current Fiscal Year	0	0
Two Years before Current Fiscal Year	0	42,067
Three Years before Current Fiscal Year	42,067	1,115
Four Years before Current Fiscal Year	5,868	0
Prior	2,199	3,364
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	50,134	46,546
Commercial lending | Real estate loan | Multifamily residential
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	160,470	783,671
Fiscal Year before Current Fiscal Year	764,482	784,324
Two Years before Current Fiscal Year	762,732	503,764
Three Years before Current Fiscal Year	493,979	418,046
Four Years before Current Fiscal Year	359,286	181,477
Prior	519,677	356,821
Revolving Loans Amortized Cost Basis	5,889	5,895
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	3,066,515	3,033,998
Commercial lending | Real estate loan | Multifamily residential | Pass
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	160,470	783,671
Fiscal Year before Current Fiscal Year	764,482	783,589
Two Years before Current Fiscal Year	762,001	479,959
Three Years before Current Fiscal Year	470,223	411,945
Four Years before Current Fiscal Year	352,094	181,213
Prior	488,260	348,751
Revolving Loans Amortized Cost Basis	5,889	5,895
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	3,003,419	2,995,023
Commercial lending | Real estate loan | Multifamily residential | Criticized (Accrual)
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year before Current Fiscal Year	0	735
Two Years before Current Fiscal Year	731	22,330
Three Years before Current Fiscal Year	22,309	6,101
Four Years before Current Fiscal Year	6,067	264
Prior	29,296	5,877
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	58,403	35,307
Commercial lending | Real estate loan | Multifamily residential | Criticized (Nonaccrual)
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year before Current Fiscal Year	0	0
Two Years before Current Fiscal Year	0	1,475
Three Years before Current Fiscal Year	1,447	0
Four Years before Current Fiscal Year	1,125	0
Prior	2,121	2,193
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	4,693	3,668
Commercial lending | Construction and land
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	9,123	228,448
Fiscal Year before Current Fiscal Year	141,475	172,707
Two Years before Current Fiscal Year	146,701	156,712
Three Years before Current Fiscal Year	121,364	0
Four Years before Current Fiscal Year	0	20,897
Prior	40,591	20,928
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	459,254	599,692
Commercial lending | Construction and land | Pass
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	5,642	224,924
Fiscal Year before Current Fiscal Year	141,475	172,707
Two Years before Current Fiscal Year	146,701	156,712
Three Years before Current Fiscal Year	121,364	0
Four Years before Current Fiscal Year	0	20,897
Prior	20,691	1,028
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	435,873	576,268
Commercial lending | Construction and land | Criticized (Accrual)
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	3,481	3,524
Fiscal Year before Current Fiscal Year	0	0
Two Years before Current Fiscal Year	0	0
Three Years before Current Fiscal Year	0	0
Four Years before Current Fiscal Year	0	0
Prior	0	19,900
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	3,481	23,424
Commercial lending | Construction and land | Criticized (Nonaccrual)
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year before Current Fiscal Year	0	0
Two Years before Current Fiscal Year	0	0
Three Years before Current Fiscal Year	0	0
Four Years before Current Fiscal Year	0	0
Prior	19,900	0
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	19,900	0
Commercial lending | Total CRE
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	863,134	3,356,227
Fiscal Year before Current Fiscal Year	3,243,890	3,422,821
Two Years before Current Fiscal Year	3,328,051	3,056,738
Three Years before Current Fiscal Year	2,935,983	1,845,671
Four Years before Current Fiscal Year	1,710,776	937,162
Prior	2,783,435	1,991,456
Revolving Loans Amortized Cost Basis	199,430	179,162
Revolving Loans Converted to Term Loans Amortized Cost Basis	24,104	19,064
Total	15,088,803	14,808,301
Consumer lending
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	670,509	2,396,531
Fiscal Year before Current Fiscal Year	2,436,288	1,815,886
Two Years before Current Fiscal Year	1,706,759	1,505,836
Three Years before Current Fiscal Year	1,390,278	1,037,797
Four Years before Current Fiscal Year	971,560	534,876
Prior	1,475,699	1,032,686
Revolving Loans Amortized Cost Basis	1,507,425	1,396,383
Revolving Loans Converted to Term Loans Amortized Cost Basis	260,317	230,933
Total	10,418,835	9,950,928
Consumer lending | Real estate loan | Single-family residential
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	669,660	2,385,853
Fiscal Year before Current Fiscal Year	2,427,430	1,814,855
Two Years before Current Fiscal Year	1,706,060	1,502,472
Three Years before Current Fiscal Year	1,386,855	1,023,496
Four Years before Current Fiscal Year	958,900	525,283
Prior	1,375,382	933,994
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	8,524,287	8,185,953
Consumer lending | Real estate loan | Single-family residential | Pass
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	669,660	2,385,853
Fiscal Year before Current Fiscal Year	2,427,430	1,813,200
Two Years before Current Fiscal Year	1,704,855	1,501,660
Three Years before Current Fiscal Year	1,385,623	1,021,707
Four Years before Current Fiscal Year	956,307	523,170
Prior	1,360,015	921,714
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	8,503,890	8,167,304
Consumer lending | Real estate loan | Single-family residential | Criticized (Accrual)
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year before Current Fiscal Year	0	1,429
Two Years before Current Fiscal Year	0	0
Three Years before Current Fiscal Year	194	0
Four Years before Current Fiscal Year	347	119
Prior	2,207	1,034
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	2,748	2,582
Consumer lending | Real estate loan | Single-family residential | Criticized (Nonaccrual)
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year before Current Fiscal Year	0	226
Two Years before Current Fiscal Year	1,205	812
Three Years before Current Fiscal Year	1,038	1,789
Four Years before Current Fiscal Year	2,246	1,994
Prior	13,160	11,246
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	17,649	16,067
Consumer lending | HELOCs
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	0	1,131
Fiscal Year before Current Fiscal Year	690	1,031
Two Years before Current Fiscal Year	699	3,364
Three Years before Current Fiscal Year	3,423	9,980
Four Years before Current Fiscal Year	8,338	9,593
Prior	16,770	15,437
Revolving Loans Amortized Cost Basis	1,458,935	1,330,247
Revolving Loans Converted to Term Loans Amortized Cost Basis	260,317	230,933
Total	1,749,172	1,601,716
Consumer lending | HELOCs | Pass
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	0	1,131
Fiscal Year before Current Fiscal Year	690	880
Two Years before Current Fiscal Year	548	2,879
Three Years before Current Fiscal Year	3,235	5,363
Four Years before Current Fiscal Year	4,319	8,433
Prior	14,931	13,475
Revolving Loans Amortized Cost Basis	1,458,199	1,328,919
Revolving Loans Converted to Term Loans Amortized Cost Basis	255,538	225,810
Total	1,737,460	1,586,890
Consumer lending | HELOCs | Criticized (Accrual)
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year before Current Fiscal Year	0	0
Two Years before Current Fiscal Year	0	200
Three Years before Current Fiscal Year	0	0
Four Years before Current Fiscal Year	0	996
Prior	1	0
Revolving Loans Amortized Cost Basis	287	1,328
Revolving Loans Converted to Term Loans Amortized Cost Basis	547	606
Total	835	3,130
Consumer lending | HELOCs | Criticized (Nonaccrual)
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year before Current Fiscal Year	0	151
Two Years before Current Fiscal Year	151	285
Three Years before Current Fiscal Year	188	4,617
Four Years before Current Fiscal Year	4,019	164
Prior	1,838	1,962
Revolving Loans Amortized Cost Basis	449	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	4,232	4,517
Total	10,877	11,696
Consumer lending | Total residential mortgage
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	669,660	2,386,984
Fiscal Year before Current Fiscal Year	2,428,120	1,815,886
Two Years before Current Fiscal Year	1,706,759	1,505,836
Three Years before Current Fiscal Year	1,390,278	1,033,476
Four Years before Current Fiscal Year	967,238	534,876
Prior	1,392,152	949,431
Revolving Loans Amortized Cost Basis	1,458,935	1,330,247
Revolving Loans Converted to Term Loans Amortized Cost Basis	260,317	230,933
Total	10,273,459	9,787,669
Consumer lending | Other consumer
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	849	9,547
Fiscal Year before Current Fiscal Year	8,168	0
Two Years before Current Fiscal Year	0	0
Three Years before Current Fiscal Year	0	4,321
Four Years before Current Fiscal Year	4,322	0
Prior	83,547	83,255
Revolving Loans Amortized Cost Basis	48,490	66,136
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	145,376	163,259
Consumer lending | Other consumer | Pass
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	849	9,531
Fiscal Year before Current Fiscal Year	8,168	0
Two Years before Current Fiscal Year	0	0
Three Years before Current Fiscal Year	0	1,830
Four Years before Current Fiscal Year	1,830	0
Prior	83,547	83,255
Revolving Loans Amortized Cost Basis	48,455	66,136
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	142,849	160,752
Consumer lending | Other consumer | Criticized (Accrual)
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year		16
Fiscal Year before Current Fiscal Year		0
Two Years before Current Fiscal Year		0
Three Years before Current Fiscal Year		0
Four Years before Current Fiscal Year		0
Prior		0
Revolving Loans Amortized Cost Basis		0
Revolving Loans Converted to Term Loans Amortized Cost Basis		0
Total		16
Consumer lending | Other consumer | Criticized (Nonaccrual)
Financing Receivable, Vintage Year/Credit Quality Indicator [Line Items]
Current Fiscal Year	0	0
Fiscal Year before Current Fiscal Year	0	0
Two Years before Current Fiscal Year	0	0
Three Years before Current Fiscal Year	0	2,491
Four Years before Current Fiscal Year	2,492	0
Prior	0	0
Revolving Loans Amortized Cost Basis	35	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	$ 2,527	$ 2,491