Allowance for Credit Losses - Commercial Real Estate and Commercial Loan Segments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	$ 1,212,344
2019	3,540,465
2018	2,369,668
2017	1,982,912
2016	1,171,944
Prior	2,385,545
Revolving	779,125
Revolving Converted to Term During the Period	8,837
Total	13,450,840	$ 8,722,311
Investor loans secured by real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	854,784
2019	2,458,374
2018	1,560,916
2017	1,114,295
2016	730,632
Prior	1,513,942
Revolving	12,538
Revolving Converted to Term During the Period	0
Total	8,245,481	4,153,084
Investor loans secured by real estate | CRE non-owner-occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	2,707,930	2,070,141
Investor loans secured by real estate | CRE non-owner-occupied | 0% - 5.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	188,404
2019	543,940
2018	374,636
2017	265,887
2016	266,967
Prior	792,295
Revolving	10,788
Revolving Converted to Term During the Period	0
Total	2,442,917
Investor loans secured by real estate | CRE non-owner-occupied | >5.00% - 10.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	7,015
2018	102,566
2017	10,874
2016	17,282
Prior	25,791
Revolving	243
Revolving Converted to Term During the Period	0
Total	163,771
Investor loans secured by real estate | CRE non-owner-occupied | Greater than 10%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	2,297
2019	15,900
2018	202
2017	37,864
2016	6,447
Prior	37,973
Revolving	559
Revolving Converted to Term During the Period	0
Total	101,242
Investor loans secured by real estate | Multifamily
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	5,142,069	1,575,726
Investor loans secured by real estate | Multifamily | 0% - 5.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	630,900
2019	1,709,927
2018	935,659
2017	723,886
2016	399,890
Prior	618,503
Revolving	574
Revolving Converted to Term During the Period	0
Total	5,019,339
Investor loans secured by real estate | Multifamily | >5.00% - 10.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	4,251
2019	11,286
2018	14,944
2017	14,708
2016	2,836
Prior	2,102
Revolving	0
Revolving Converted to Term During the Period	0
Total	50,127
Investor loans secured by real estate | Multifamily | Greater than 10%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	3,198
2019	14,022
2018	14,137
2017	12,513
2016	10,167
Prior	18,566
Revolving	0
Revolving Converted to Term During the Period	0
Total	72,603
Investor loans secured by real estate | Construction and land
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	337,872	438,786
Investor loans secured by real estate | Construction and land | 0% - 5.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	24,862
2019	56,858
2018	12,550
2017	22,362
2016	0
Prior	6,448
Revolving	0
Revolving Converted to Term During the Period	0
Total	123,080
Investor loans secured by real estate | Construction and land | >5.00% - 10.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	36,289
2018	10,750
2017	466
2016	0
Prior	0
Revolving	0
Revolving Converted to Term During the Period	0
Total	47,505
Investor loans secured by real estate | Construction and land | Greater than 10%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	378
2019	52,562
2018	82,297
2017	10,195
2016	19,932
Prior	1,549
Revolving	374
Revolving Converted to Term During the Period	0
Total	167,287
Investor loans secured by real estate | SBA secured by real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	57,610	68,431
Investor loans secured by real estate | SBA secured by real estate | 0% - 5.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	494
2019	10,412
2018	12,584
2017	15,540
2016	7,111
Prior	10,204
Revolving	0
Revolving Converted to Term During the Period	0
Total	56,345
Investor loans secured by real estate | SBA secured by real estate | >5.00% - 10.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving	0
Revolving Converted to Term During the Period	0
Total	0
Investor loans secured by real estate | SBA secured by real estate | Greater than 10%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	163
2018	591
2017	0
2016	0
Prior	511
Revolving	0
Revolving Converted to Term During the Period	0
Total	1,265
Business loans secured by real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	233,812
2019	523,420
2018	450,328
2017	479,759
2016	283,961
Prior	587,025
Revolving	4,938
Revolving Converted to Term During the Period	0
Total	2,563,243	2,288,175
Business loans secured by real estate | SBA secured by real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	84,126	88,381
Business loans secured by real estate | SBA secured by real estate | 0% - 5.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	2,643
2019	7,658
2018	13,375
2017	15,993
2016	6,150
Prior	22,077
Revolving	95
Revolving Converted to Term During the Period	0
Total	67,991
Business loans secured by real estate | SBA secured by real estate | >5.00% - 10.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	0
2018	679
2017	1,117
2016	3,493
Prior	4,679
Revolving	0
Revolving Converted to Term During the Period	0
Total	9,968
Business loans secured by real estate | SBA secured by real estate | Greater than 10%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	0
2018	22
2017	1,994
2016	914
Prior	3,237
Revolving	0
Revolving Converted to Term During the Period	0
Total	6,167
Business loans secured by real estate | CRE owner-occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	2,119,788	1,846,554
Business loans secured by real estate | CRE owner-occupied | 0% - 5.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	202,228
2019	368,034
2018	299,843
2017	296,647
2016	197,043
Prior	426,513
Revolving	520
Revolving Converted to Term During the Period	0
Total	1,790,828
Business loans secured by real estate | CRE owner-occupied | >5.00% - 10.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	8,434
2019	37,617
2018	58,314
2017	53,967
2016	39,056
Prior	78,666
Revolving	3,826
Revolving Converted to Term During the Period	0
Total	279,880
Business loans secured by real estate | CRE owner-occupied | Greater than 10%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	22,362
2018	3,636
2017	7,285
2016	5,793
Prior	9,507
Revolving	497
Revolving Converted to Term During the Period	0
Total	49,080
Business loans secured by real estate | Franchise real estate secured
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	359,329	353,240
Business loans secured by real estate | Franchise real estate secured | 0% - 5.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	19,753
2019	85,363
2018	73,100
2017	102,756
2016	31,512
Prior	42,346
Revolving	0
Revolving Converted to Term During the Period	0
Total	354,830
Business loans secured by real estate | Franchise real estate secured | >5.00% - 10.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	754
2019	0
2018	631
2017	0
2016	0
Prior	0
Revolving	0
Revolving Converted to Term During the Period	0
Total	1,385
Business loans secured by real estate | Franchise real estate secured | Greater than 10%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	2,386
2018	728
2017	0
2016	0
Prior	0
Revolving	0
Revolving Converted to Term During the Period	0
Total	3,114
Commercial loans
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	119,216
2019	550,144
2018	343,392
2017	335,937
2016	122,265
Prior	147,157
Revolving	726,775
Revolving Converted to Term During the Period	8,837
Total	2,353,723	1,975,053
Commercial loans | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	1,820,995	1,393,270
Commercial loans | Commercial and industrial | 0% - 5.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	90,745
2019	289,250
2018	141,811
2017	206,524
2016	49,843
Prior	76,628
Revolving	343,482
Revolving Converted to Term During the Period	4,024
Total	1,202,307
Commercial loans | Commercial and industrial | >5.00% - 10.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	7,911
2019	48,778
2018	39,716
2017	19,950
2016	18,894
Prior	14,807
Revolving	302,843
Revolving Converted to Term During the Period	2,037
Total	454,936
Commercial loans | Commercial and industrial | Greater than 10%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	6,061
2018	41,726
2017	23,095
2016	5,340
Prior	7,178
Revolving	78,355
Revolving Converted to Term During the Period	1,997
Total	163,752
Commercial loans | Franchise non-real estate secured
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	515,980	564,357
Commercial loans | Franchise non-real estate secured | 0% - 5.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	14,547
2019	193,899
2018	112,760
2017	48,916
2016	45,265
Prior	40,753
Revolving	1,361
Revolving Converted to Term During the Period	511
Total	458,012
Commercial loans | Franchise non-real estate secured | >5.00% - 10.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	5,658
2019	7,722
2018	4,353
2017	4,245
2016	2,025
Prior	2,486
Revolving	0
Revolving Converted to Term During the Period	0
Total	26,489
Commercial loans | Franchise non-real estate secured | Greater than 10%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	2,050
2018	957
2017	28,472
2016	0
Prior	0
Revolving	0
Revolving Converted to Term During the Period	0
Total	31,479
Commercial loans | SBA non-real estate secured
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	16,748	$ 17,426
Commercial loans | SBA non-real estate secured | 0% - 5.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	355
2019	2,299
2018	1,392
2017	1,460
2016	499
Prior	2,571
Revolving	0
Revolving Converted to Term During the Period	268
Total	8,844
Commercial loans | SBA non-real estate secured | >5.00% - 10.00%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	0
2018	308
2017	796
2016	124
Prior	1,285
Revolving	0
Revolving Converted to Term During the Period	0
Total	2,513
Commercial loans | SBA non-real estate secured | Greater than 10%
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	85
2018	369
2017	2,479
2016	275
Prior	1,449
Revolving	734
Revolving Converted to Term During the Period	0
Total	5,391
Commercial loans | Total commercial loans
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	119,216
2019	550,144
2018	343,392
2017	335,937
2016	122,265
Prior	147,157
Revolving	726,775
Revolving Converted to Term During the Period	8,837
Total	$ 2,353,723