Loans Receivable and Allowance for Credit Losses (Aging Analysis on Non-PCI Loans) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Nonaccrual and Past Due Loans
Number of days beyond loan classified nonaccrual	90 days
Total loans	$ 31,210,185	$ 28,975,718
Commercial lending
Nonaccrual and Past Due Loans
Total loans	23,474,977	22,210,001
Commercial lending | Commercial and industrial (“C&I”)
Nonaccrual and Past Due Loans
Total loans	11,517,054	10,697,231
Commercial lending | Commercial real estate (“CRE”)
Nonaccrual and Past Due Loans
Total loans	9,262,327	8,936,897
Commercial lending | Real estate loan | Multifamily residential
Nonaccrual and Past Due Loans
Total loans	2,090,563	1,916,176
Commercial lending | Construction and land
Nonaccrual and Past Due Loans
Total loans	605,033	659,697
Consumer lending
Nonaccrual and Past Due Loans
Total loans	7,735,208	6,765,717
Consumer lending | Real estate loan | Single-family residential
Nonaccrual and Past Due Loans
Total loans	5,684,587	4,646,289
Consumer lending | HELOCs
Nonaccrual and Past Due Loans
Total loans	1,717,440	1,782,924
Consumer lending | Other consumer
Nonaccrual and Past Due Loans
Total loans	333,181	336,504
Non-PCI Loans
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	85,732	67,677
Total Nonaccrual Loans	113,895	114,309
Current Accruing Loans	30,665,534	28,311,445
Total loans	30,865,161	28,493,431
Non-PCI Loans | Accruing Loans 30-59 Days Past Due
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	71,956	57,551
Non-PCI Loans | Accruing Loans 60-89 Days Past Due
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	13,776	10,126
Non-PCI Loans | Nonaccrual Loans 90 or More Days Past Due
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	70,568	79,958
Non-PCI Loans | Nonaccrual Loans Less Than 90 Days Past Due
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	43,327	34,351
Non-PCI Loans | Commercial lending
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	54,990	40,544
Total Nonaccrual Loans	99,310	101,889
Current Accruing Loans	23,086,687	21,716,666
Total loans	23,240,987	21,859,099
Non-PCI Loans | Commercial lending | Commercial and industrial (“C&I”)
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	27,424	31,046
Total Nonaccrual Loans	72,797	69,213
Current Accruing Loans	11,414,419	10,585,177
Total loans	11,514,640	10,685,436
Non-PCI Loans | Commercial lending | Commercial real estate (“CRE”)
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	21,190	3,880
Total Nonaccrual Loans	24,752	26,986
Current Accruing Loans	9,023,937	8,628,343
Total loans	9,069,879	8,659,209
Non-PCI Loans | Commercial lending | Real estate loan | Multifamily residential
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	4,092	4,860
Total Nonaccrual Loans	1,761	1,717
Current Accruing Loans	2,045,624	1,848,551
Total loans	2,051,477	1,855,128
Non-PCI Loans | Commercial lending | Construction and land
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	2,284	758
Total Nonaccrual Loans	0	3,973
Current Accruing Loans	602,707	654,595
Total loans	604,991	659,326
Non-PCI Loans | Commercial lending | Accruing Loans 30-59 Days Past Due
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	46,820	39,982
Non-PCI Loans | Commercial lending | Accruing Loans 30-59 Days Past Due | Commercial and industrial (“C&I”)
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	19,281	30,964
Non-PCI Loans | Commercial lending | Accruing Loans 30-59 Days Past Due | Commercial real estate (“CRE”)
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	21,163	3,414
Non-PCI Loans | Commercial lending | Accruing Loans 30-59 Days Past Due | Real estate loan | Multifamily residential
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	4,092	4,846
Non-PCI Loans | Commercial lending | Accruing Loans 30-59 Days Past Due | Construction and land
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	2,284	758
Non-PCI Loans | Commercial lending | Accruing Loans 60-89 Days Past Due
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	8,170	562
Non-PCI Loans | Commercial lending | Accruing Loans 60-89 Days Past Due | Commercial and industrial (“C&I”)
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	8,143	82
Non-PCI Loans | Commercial lending | Accruing Loans 60-89 Days Past Due | Commercial real estate (“CRE”)
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	27	466
Non-PCI Loans | Commercial lending | Accruing Loans 60-89 Days Past Due | Real estate loan | Multifamily residential
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	0	14
Non-PCI Loans | Commercial lending | Accruing Loans 60-89 Days Past Due | Construction and land
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	0	0
Non-PCI Loans | Commercial lending | Nonaccrual Loans 90 or More Days Past Due
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	57,949	67,633
Non-PCI Loans | Commercial lending | Nonaccrual Loans 90 or More Days Past Due | Commercial and industrial (“C&I”)
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	38,014	41,805
Non-PCI Loans | Commercial lending | Nonaccrual Loans 90 or More Days Past Due | Commercial real estate (“CRE”)
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	19,266	21,556
Non-PCI Loans | Commercial lending | Nonaccrual Loans 90 or More Days Past Due | Real estate loan | Multifamily residential
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	669	299
Non-PCI Loans | Commercial lending | Nonaccrual Loans 90 or More Days Past Due | Construction and land
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	0	3,973
Non-PCI Loans | Commercial lending | Nonaccrual Loans Less Than 90 Days Past Due
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	41,361	34,256
Non-PCI Loans | Commercial lending | Nonaccrual Loans Less Than 90 Days Past Due | Commercial and industrial (“C&I”)
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	34,783	27,408
Non-PCI Loans | Commercial lending | Nonaccrual Loans Less Than 90 Days Past Due | Commercial real estate (“CRE”)
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	5,486	5,430
Non-PCI Loans | Commercial lending | Nonaccrual Loans Less Than 90 Days Past Due | Real estate loan | Multifamily residential
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	1,092	1,418
Non-PCI Loans | Commercial lending | Nonaccrual Loans Less Than 90 Days Past Due | Construction and land
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	0	0
Non-PCI Loans | Consumer lending
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	30,742	27,133
Total Nonaccrual Loans	14,585	12,420
Current Accruing Loans	7,578,847	6,594,779
Total loans	7,624,174	6,634,332
Non-PCI Loans | Consumer lending | Real estate loan | Single-family residential
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	23,553	18,624
Total Nonaccrual Loans	5,222	5,923
Current Accruing Loans	5,554,420	4,504,364
Total loans	5,583,195	4,528,911
Non-PCI Loans | Consumer lending | HELOCs
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	7,177	8,472
Total Nonaccrual Loans	6,872	4,006
Current Accruing Loans	1,693,749	1,756,439
Total loans	1,707,798	1,768,917
Non-PCI Loans | Consumer lending | Other consumer
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	12	37
Total Nonaccrual Loans	2,491	2,491
Current Accruing Loans	330,678	333,976
Total loans	333,181	336,504
Non-PCI Loans | Consumer lending | Accruing Loans 30-59 Days Past Due
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	25,136	17,569
Non-PCI Loans | Consumer lending | Accruing Loans 30-59 Days Past Due | Real estate loan | Single-family residential
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	20,435	13,269
Non-PCI Loans | Consumer lending | Accruing Loans 30-59 Days Past Due | HELOCs
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	4,695	4,286
Non-PCI Loans | Consumer lending | Accruing Loans 30-59 Days Past Due | Other consumer
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	6	14
Non-PCI Loans | Consumer lending | Accruing Loans 60-89 Days Past Due
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	5,606	9,564
Non-PCI Loans | Consumer lending | Accruing Loans 60-89 Days Past Due | Real estate loan | Single-family residential
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	3,118	5,355
Non-PCI Loans | Consumer lending | Accruing Loans 60-89 Days Past Due | HELOCs
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	2,482	4,186
Non-PCI Loans | Consumer lending | Accruing Loans 60-89 Days Past Due | Other consumer
Nonaccrual and Past Due Loans
Total Accruing Past Due Loans	6	23
Non-PCI Loans | Consumer lending | Nonaccrual Loans 90 or More Days Past Due
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	12,619	12,325
Non-PCI Loans | Consumer lending | Nonaccrual Loans 90 or More Days Past Due | Real estate loan | Single-family residential
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	4,813	5,917
Non-PCI Loans | Consumer lending | Nonaccrual Loans 90 or More Days Past Due | HELOCs
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	5,315	3,917
Non-PCI Loans | Consumer lending | Nonaccrual Loans 90 or More Days Past Due | Other consumer
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	2,491	2,491
Non-PCI Loans | Consumer lending | Nonaccrual Loans Less Than 90 Days Past Due
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	1,966	95
Non-PCI Loans | Consumer lending | Nonaccrual Loans Less Than 90 Days Past Due | Real estate loan | Single-family residential
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	409	6
Non-PCI Loans | Consumer lending | Nonaccrual Loans Less Than 90 Days Past Due | HELOCs
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	1,557	89
Non-PCI Loans | Consumer lending | Nonaccrual Loans Less Than 90 Days Past Due | Other consumer
Nonaccrual and Past Due Loans
Total Nonaccrual Loans	$ 0	$ 0