Loans - Balances Of Commercial Loan Portfolio Classes, Disaggregated By PD Grade (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Allowance	$ 184,911	$ 180,424	$ 187,194	$ 189,555
Total loans collectively evaluated for impairment	27,638,617		26,847,384
Total loans individually evaluated for impairment	275,148		249,602
Purchased credit-impaired loans	76,283		152,807
Allowance - collectively evaluated for impairment	153,692		145,365
Allowance - individually evaluated for impairment	27,806		39,274
Allowance - purchased credit-impaired loans	$ 3,413	$ 4,000	2,555
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percent of total commercial loans (percent)	100.00%	100.00%
Loans and Leases Receivable, Allowance	$ 138,095	$ 130,258
Total loans collectively evaluated for impairment	20,992,761	20,437,747
Total loans individually evaluated for impairment	85,132	50,558
Purchased credit-impaired loans	45,162	56,893
Total commercial loans	$ 21,123,055	$ 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	$ 132,517	$ 126,361
Allowance - individually evaluated for impairment	3,437	1,074
Allowance - purchased credit-impaired loans	2,141	2,823
Commercial Loan P D Grade One | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 647,270	$ 622,763
Percent of total commercial loans (percent)	3.00%	3.00%
Loans and Leases Receivable, Allowance	$ 100	$ 100
Commercial Loan P D Grade Two | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 851,828	$ 837,493
Percent of total commercial loans (percent)	4.00%	4.00%
Loans and Leases Receivable, Allowance	$ 267	$ 274
Commercial Loan P D Grade Three | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 1,705,269	$ 1,789,074
Percent of total commercial loans (percent)	8.00%	9.00%
Loans and Leases Receivable, Allowance	$ 338	$ 315
Commercial Loan P D Grade Four | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 2,225,071	$ 2,224,417
Percent of total commercial loans (percent)	11.00%	11.00%
Loans and Leases Receivable, Allowance	$ 806	$ 686
Commercial Loan P D Grade Five | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 3,224,216	$ 3,088,258
Percent of total commercial loans (percent)	15.00%	15.00%
Loans and Leases Receivable, Allowance	$ 10,033	$ 8,919
Commercial Loan P D Grade Six | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 3,107,562	$ 2,824,473
Percent of total commercial loans (percent)	15.00%	14.00%
Loans and Leases Receivable, Allowance	$ 9,700	$ 8,141
Commercial Loan P D Grade Seven | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 3,475,528	$ 3,363,877
Percent of total commercial loans (percent)	17.00%	16.00%
Loans and Leases Receivable, Allowance	$ 18,677	$ 16,906
Commercial Loan P D Grade Eight | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 1,821,908	$ 1,676,558
Percent of total commercial loans (percent)	9.00%	8.00%
Loans and Leases Receivable, Allowance	$ 20,047	$ 18,545
Commercial Loan P D Grade Nine | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 2,005,281	$ 2,099,294
Percent of total commercial loans (percent)	9.00%	10.00%
Loans and Leases Receivable, Allowance	$ 16,042	$ 15,454
Commercial Loan P D Grade Ten | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 600,122	$ 587,305
Percent of total commercial loans (percent)	3.00%	3.00%
Loans and Leases Receivable, Allowance	$ 8,739	$ 8,675
Commercial Loan P D Grade Eleven | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 460,823	$ 379,741
Percent of total commercial loans (percent)	2.00%	2.00%
Loans and Leases Receivable, Allowance	$ 10,353	$ 7,973
Commercial Loan P D Grade Twelve | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 343,389	$ 342,537
Percent of total commercial loans (percent)	2.00%	2.00%
Loans and Leases Receivable, Allowance	$ 6,172	$ 6,972
Commercial Loan P D Grade Thirteen | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 281,001	$ 347,432
Percent of total commercial loans (percent)	1.00%	2.00%
Loans and Leases Receivable, Allowance	$ 9,652	$ 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	$ 243,493	$ 254,525
Percent of total commercial loans (percent)	1.00%	1.00%
Loans and Leases Receivable, Allowance	$ 21,591	$ 23,307
C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Allowance	103,713	98,947	100,238	98,211
Total loans collectively evaluated for impairment	17,056,034		15,705,895
Total loans individually evaluated for impairment	83,253		40,758
Purchased credit-impaired loans	36,825		81,655
Allowance - collectively evaluated for impairment	98,135		93,603
Allowance - individually evaluated for impairment	3,437		4,555
Allowance - purchased credit-impaired loans	2,141		2,080
C&I | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans collectively evaluated for impairment	14,508,130	14,152,795
Total loans individually evaluated for impairment	80,415	45,704
Purchased credit-impaired loans	36,825	41,730
Total commercial loans	14,625,370	14,240,229
C&I | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans collectively evaluated for impairment	2,301,340	2,023,746
Total loans individually evaluated for impairment	0	0
Purchased credit-impaired loans	0	0
Total commercial loans	2,301,340	2,023,746
C&I | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans collectively evaluated for impairment	246,564	247,465
Total loans individually evaluated for impairment	2,838	2,888
Purchased credit-impaired loans	0	0
Total commercial loans	249,402	250,353
Valuation allowance	20,200	20,200
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	635,273	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	849,658	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	720,323	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	689,936	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	1,201,020	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	478,359	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	32,498	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	1,904,650	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	347,923	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	96,052	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	1,992,100	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	400,889	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	33,815	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	2,794,923	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	94,626	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	11,446	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	1,344,591	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	172,050	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	1,460,633	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	104,832	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	45,117	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	492,043	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	12,579	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	395,393	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	289,203	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	146	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	223,362	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	5,786	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	204,958	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	34,382	31,311	29,057	$ 28,427
Total loans collectively evaluated for impairment	3,936,727		4,201,220
Total loans individually evaluated for impairment	1,879		2,077
Purchased credit-impaired loans	8,337		31,138
Allowance - collectively evaluated for impairment	34,382		28,869
Allowance - individually evaluated for impairment	0		0
Allowance - purchased credit-impaired loans	0		$ 188
Commercial real estate | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans collectively evaluated for impairment	3,786,183	3,877,848
Total loans individually evaluated for impairment	1,879	1,966
Purchased credit-impaired loans	6,043	12,730
Total commercial loans	3,794,105	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	150,544	135,893
Total loans individually evaluated for impairment	0	0
Purchased credit-impaired loans	2,294	2,433
Total commercial loans	152,838	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	11,997	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	2,144	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	26	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	291,517	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	179	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	513,082	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	112	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	855,280	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	20,311	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	636,472	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	44,286	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	544,211	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	30,322	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	280,323	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	24,944	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	377,027	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	17,672	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	73,040	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	3,924	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	63,318	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	2,112	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	48,454	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	5,586	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	51,615	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	238	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	37,703	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	$ 832	$ 837