Loans - Balances Of Commercial Loan Portfolio Classes, Disaggregated By PD Grade (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Allowance	$ 200,307	$ 180,424	$ 189,555		$ 202,068
Total loans collectively evaluated for impairment	30,758,025	27,204,542	27,219,667
Total loans individually evaluated for impairment	246,900	240,533	259,713
Purchased credit-impaired loans	56,186	90,457	179,549
Allowance - collectively evaluated for impairment	172,426	147,573	144,620
Allowance - individually evaluated for impairment	25,916	28,814	41,767
Allowance - purchased credit-impaired loans	1,965	4,037	3,168
Gain on sale of TRUPs loans	$ 1,105	$ 3,777	0
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percent of total commercial loans (percent)	100.00%	100.00%
Loans and Leases Receivable, Allowance	$ 158,598	$ 130,258
Total loans collectively evaluated for impairment	24,273,207	20,437,747
Total loans individually evaluated for impairment	84,001	50,558
Purchased credit-impaired loans	30,900	56,893
Total commercial loans	$ 24,388,108	$ 20,545,198
Percent of loan collectively evaluated for impairment (percent)	100.00%	100.00%
Percent of loan individually evaluated for impairment (percent)	0.00%	0.00%
Percent of loan purchased-credit impaired (percent)	0.00%	0.00%
Allowance - collectively evaluated for impairment	$ 151,554	$ 126,361
Allowance - individually evaluated for impairment	6,196	1,074
Allowance - purchased credit-impaired loans	848	2,823
Commercial Loan P D Grade One | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	$ 697,888	$ 622,763
Percent of total commercial loans (percent)	3.00%	3.00%
Loans and Leases Receivable, Allowance	$ 69	$ 100
Commercial Loan P D Grade Two | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	$ 815,992	$ 837,493
Percent of total commercial loans (percent)	4.00%	4.00%
Loans and Leases Receivable, Allowance	$ 165	$ 274
Commercial Loan P D Grade Three | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	$ 2,098,520	$ 1,789,074
Percent of total commercial loans (percent)	9.00%	9.00%
Loans and Leases Receivable, Allowance	$ 274	$ 315
Commercial Loan P D Grade Four | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	$ 2,657,818	$ 2,224,417
Percent of total commercial loans (percent)	11.00%	11.00%
Loans and Leases Receivable, Allowance	$ 738	$ 686
Commercial Loan P D Grade Five | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	$ 3,725,003	$ 3,088,258
Percent of total commercial loans (percent)	15.00%	15.00%
Loans and Leases Receivable, Allowance	$ 8,265	$ 8,919
Commercial Loan P D Grade Six | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	$ 4,683,029	$ 2,824,473
Percent of total commercial loans (percent)	19.00%	14.00%
Loans and Leases Receivable, Allowance	$ 12,054	$ 8,141
Commercial Loan P D Grade Seven | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	$ 3,908,971	$ 3,363,877
Percent of total commercial loans (percent)	16.00%	16.00%
Loans and Leases Receivable, Allowance	$ 20,409	$ 16,906
Commercial Loan P D Grade Eight | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	$ 2,166,241	$ 1,676,558
Percent of total commercial loans (percent)	9.00%	8.00%
Loans and Leases Receivable, Allowance	$ 22,514	$ 18,545
Commercial Loan P D Grade Nine | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	$ 1,393,514	$ 2,099,294
Percent of total commercial loans (percent)	6.00%	10.00%
Loans and Leases Receivable, Allowance	$ 17,484	$ 15,454
Commercial Loan P D Grade Ten | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	$ 665,145	$ 587,305
Percent of total commercial loans (percent)	3.00%	3.00%
Loans and Leases Receivable, Allowance	$ 10,197	$ 8,675
Commercial Loan P D Grade Eleven | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	$ 579,124	$ 379,741
Percent of total commercial loans (percent)	2.00%	2.00%
Loans and Leases Receivable, Allowance	$ 13,454	$ 7,973
Commercial Loan P D Grade Twelve | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	$ 307,945	$ 342,537
Percent of total commercial loans (percent)	1.00%	2.00%
Loans and Leases Receivable, Allowance	$ 8,471	$ 6,972
Commercial Loan P D Grade Thirteen | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	$ 266,915	$ 347,432
Percent of total commercial loans (percent)	1.00%	2.00%
Loans and Leases Receivable, Allowance	$ 8,142	$ 10,094
Commercial Loan P D Grade Fourteen Fifteen Sixteen | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	$ 307,102	$ 254,525
Percent of total commercial loans (percent)	1.00%	1.00%
Loans and Leases Receivable, Allowance	$ 29,318	$ 23,307
C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Allowance	122,486	98,947	98,211		89,398
Total loans collectively evaluated for impairment	19,942,728	16,424,006	15,909,110
Total loans individually evaluated for impairment	82,438	48,592	43,024
Purchased credit-impaired loans	25,925	41,730	105,139
Allowance - collectively evaluated for impairment	115,442	95,050	89,358
Allowance - individually evaluated for impairment	6,196	1,074	6,044
Allowance - purchased credit-impaired loans	848	2,823	2,809
C&I | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans collectively evaluated for impairment	15,313,558	14,152,795
Total loans individually evaluated for impairment	82,438	45,704
Purchased credit-impaired loans	25,925	41,730
Total commercial loans	15,421,921	14,240,229
C&I | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans collectively evaluated for impairment	4,410,883	2,023,746
Total loans individually evaluated for impairment	0	0
Purchased credit-impaired loans	0	0
Total commercial loans	4,410,883	2,023,746
C&I | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans collectively evaluated for impairment	218,287	247,465
Total loans individually evaluated for impairment	0	2,888
Purchased credit-impaired loans	0	0
Total commercial loans	218,287	250,353
Valuation allowance	19,100	20,200
Gain on sale of TRUPs loans		3,800
Financing receivable, sold		3,000		$ 55,500
Financing receivable sold, allowance		300		$ 5,000
C&I | Commercial Loan P D Grade One | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	696,040	610,177
C&I | Commercial Loan P D Grade One | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	0	0
C&I | Commercial Loan P D Grade One | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	0	0
C&I | Commercial Loan P D Grade Two | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	767,048	835,776
C&I | Commercial Loan P D Grade Two | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	0	0
C&I | Commercial Loan P D Grade Two | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	0	0
C&I | Commercial Loan P D Grade Three | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	743,123	782,362
C&I | Commercial Loan P D Grade Three | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	877,210	716,971
C&I | Commercial Loan P D Grade Three | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	3,314	0
C&I | Commercial Loan P D Grade Four | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	1,237,772	1,223,092
C&I | Commercial Loan P D Grade Four | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	692,971	394,862
C&I | Commercial Loan P D Grade Four | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	46,375	43,220
C&I | Commercial Loan P D Grade Five | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	1,986,761	1,920,034
C&I | Commercial Loan P D Grade Five | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	670,402	277,814
C&I | Commercial Loan P D Grade Five | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	72,512	77,751
C&I | Commercial Loan P D Grade Six | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	2,511,290	1,722,136
C&I | Commercial Loan P D Grade Six | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	1,410,387	365,341
C&I | Commercial Loan P D Grade Six | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	27,263	45,609
C&I | Commercial Loan P D Grade Seven | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	2,708,707	2,690,784
C&I | Commercial Loan P D Grade Seven | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	509,616	96,603
C&I | Commercial Loan P D Grade Seven | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	18,378	11,446
C&I | Commercial Loan P D Grade Eight | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	1,743,364	1,337,113
C&I | Commercial Loan P D Grade Eight | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	136,771	53,224
C&I | Commercial Loan P D Grade Eight | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	0	0
C&I | Commercial Loan P D Grade Nine | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	1,101,873	1,472,852
C&I | Commercial Loan P D Grade Nine | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	77,139	96,292
C&I | Commercial Loan P D Grade Nine | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	31,909	45,117
C&I | Commercial Loan P D Grade Ten | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	563,635	490,795
C&I | Commercial Loan P D Grade Ten | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	21,229	13,260
C&I | Commercial Loan P D Grade Ten | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	18,536	18,536
C&I | Commercial Loan P D Grade Eleven | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	495,140	311,967
C&I | Commercial Loan P D Grade Eleven | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	0	0
C&I | Commercial Loan P D Grade Eleven | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	0	0
C&I | Commercial Loan P D Grade Twelve | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	262,906	244,867
C&I | Commercial Loan P D Grade Twelve | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	15,158	9,379
C&I | Commercial Loan P D Grade Twelve | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	0	0
C&I | Commercial Loan P D Grade Thirteen | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	232,823	285,987
C&I | Commercial Loan P D Grade Thirteen | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	0	0
C&I | Commercial Loan P D Grade Thirteen | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	0	5,786
C&I | Commercial Loan P D Grade Fourteen Fifteen Sixteen | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	263,076	224,853
C&I | Commercial Loan P D Grade Fourteen Fifteen Sixteen | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	0	0
C&I | Commercial Loan P D Grade Fourteen Fifteen Sixteen | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	0	0
Commercial real estate | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Allowance	36,112	31,311	28,427		$ 33,852
Total loans collectively evaluated for impairment	4,330,479	4,013,741	4,181,908
Total loans individually evaluated for impairment	1,563	1,966	2,407
Purchased credit-impaired loans	4,975	15,163	30,380
Allowance - collectively evaluated for impairment	36,112	31,311	28,291
Allowance - individually evaluated for impairment	0	0	132
Allowance - purchased credit-impaired loans	0	0	$ 4
Commercial real estate | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans collectively evaluated for impairment	4,242,519	3,877,848
Total loans individually evaluated for impairment	1,563	1,966
Purchased credit-impaired loans	4,155	12,730
Total commercial loans	4,248,237	3,892,544
Commercial real estate | Residential C R E | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans collectively evaluated for impairment	87,960	135,893
Total loans individually evaluated for impairment	0	0
Purchased credit-impaired loans	820	2,433
Total commercial loans	88,780	138,326
Commercial real estate | Commercial Loan P D Grade One | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	1,848	12,586
Commercial real estate | Commercial Loan P D Grade One | Residential C R E | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	0	0
Commercial real estate | Commercial Loan P D Grade Two | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	48,906	1,688
Commercial real estate | Commercial Loan P D Grade Two | Residential C R E | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	38	29
Commercial real estate | Commercial Loan P D Grade Three | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	474,067	289,594
Commercial real estate | Commercial Loan P D Grade Three | Residential C R E | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	806	147
Commercial real estate | Commercial Loan P D Grade Four | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	680,223	563,243
Commercial real estate | Commercial Loan P D Grade Four | Residential C R E | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	477	0
Commercial real estate | Commercial Loan P D Grade Five | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	993,628	798,509
Commercial real estate | Commercial Loan P D Grade Five | Residential C R E | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	1,700	14,150
Commercial real estate | Commercial Loan P D Grade Six | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	717,062	657,628
Commercial real estate | Commercial Loan P D Grade Six | Residential C R E | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	17,027	33,759
Commercial real estate | Commercial Loan P D Grade Seven | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	641,345	538,909
Commercial real estate | Commercial Loan P D Grade Seven | Residential C R E | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	30,925	26,135
Commercial real estate | Commercial Loan P D Grade Eight | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	269,407	265,901
Commercial real estate | Commercial Loan P D Grade Eight | Residential C R E | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	16,699	20,320
Commercial real estate | Commercial Loan P D Grade Nine | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	169,586	455,184
Commercial real estate | Commercial Loan P D Grade Nine | Residential C R E | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	13,007	29,849
Commercial real estate | Commercial Loan P D Grade Ten | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	59,592	60,803
Commercial real estate | Commercial Loan P D Grade Ten | Residential C R E | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	2,153	3,911
Commercial real estate | Commercial Loan P D Grade Eleven | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	81,682	66,986
Commercial real estate | Commercial Loan P D Grade Eleven | Residential C R E | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	2,302	788
Commercial real estate | Commercial Loan P D Grade Twelve | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	28,807	82,574
Commercial real estate | Commercial Loan P D Grade Twelve | Residential C R E | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	1,074	5,717
Commercial real estate | Commercial Loan P D Grade Thirteen | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	32,966	55,408
Commercial real estate | Commercial Loan P D Grade Thirteen | Residential C R E | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	1,126	251
Commercial real estate | Commercial Loan P D Grade Fourteen Fifteen Sixteen | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	43,400	28,835
Commercial real estate | Commercial Loan P D Grade Fourteen Fifteen Sixteen | Residential C R E | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, Disaggregated by PD grade	$ 626	$ 837