Loans - Balances Of Commercial Loan Portfolio Classes, Disaggregated By PD Grade (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Allowance	$ 192,749	$ 184,911	$ 180,424	$ 185,462	$ 187,194	$ 189,555
Total loans collectively evaluated for impairment	29,343,285			27,344,254
Total loans individually evaluated for impairment	300,726			234,651
Purchased credit-impaired loans	68,799			122,835
Allowance - collectively evaluated for impairment	159,579			149,751
Allowance - individually evaluated for impairment	31,181			32,704
Allowance - purchased credit-impaired loans	$ 1,989		$ 4,000	3,007
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percent of total commercial loans (percent)	100.00%		100.00%
Loans and Leases Receivable, Allowance	$ 149,049		$ 130,258
Total loans collectively evaluated for impairment	22,756,648		20,437,747
Total loans individually evaluated for impairment	117,585		50,558
Purchased credit-impaired loans	41,067		56,893
Total commercial loans	$ 22,915,300		$ 20,545,198
Percent of loan collectively evaluated for impairment (percent)	99.00%		100.00%
Percent of loan individually evaluated for impairment (percent)	1.00%		0.00%
Percent of loan purchased-credit impaired (percent)	0.00%		0.00%
Allowance - collectively evaluated for impairment	$ 139,711		$ 126,361
Allowance - individually evaluated for impairment	8,484		1,074
Allowance - purchased credit-impaired loans	854		2,823
Commercial Loan P D Grade One | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 657,091		$ 622,763
Percent of total commercial loans (percent)	3.00%		3.00%
Loans and Leases Receivable, Allowance	$ 77		$ 100
Commercial Loan P D Grade Two | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 792,290		$ 837,493
Percent of total commercial loans (percent)	3.00%		4.00%
Loans and Leases Receivable, Allowance	$ 214		$ 274
Commercial Loan P D Grade Three | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 2,105,439		$ 1,789,074
Percent of total commercial loans (percent)	9.00%		9.00%
Loans and Leases Receivable, Allowance	$ 313		$ 315
Commercial Loan P D Grade Four | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 2,535,719		$ 2,224,417
Percent of total commercial loans (percent)	11.00%		11.00%
Loans and Leases Receivable, Allowance	$ 891		$ 686
Commercial Loan P D Grade Five | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 3,712,665		$ 3,088,258
Percent of total commercial loans (percent)	16.00%		15.00%
Loans and Leases Receivable, Allowance	$ 10,548		$ 8,919
Commercial Loan P D Grade Six | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 3,843,148		$ 2,824,473
Percent of total commercial loans (percent)	17.00%		14.00%
Loans and Leases Receivable, Allowance	$ 11,608		$ 8,141
Commercial Loan P D Grade Seven | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 3,642,856		$ 3,363,877
Percent of total commercial loans (percent)	16.00%		16.00%
Loans and Leases Receivable, Allowance	$ 20,083		$ 16,906
Commercial Loan P D Grade Eight | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 1,951,115		$ 1,676,558
Percent of total commercial loans (percent)	9.00%		8.00%
Loans and Leases Receivable, Allowance	$ 20,579		$ 18,545
Commercial Loan P D Grade Nine | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 1,616,866		$ 2,099,294
Percent of total commercial loans (percent)	7.00%		10.00%
Loans and Leases Receivable, Allowance	$ 18,284		$ 15,454
Commercial Loan P D Grade Ten | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 670,737		$ 587,305
Percent of total commercial loans (percent)	3.00%		3.00%
Loans and Leases Receivable, Allowance	$ 9,312		$ 8,675
Commercial Loan P D Grade Eleven | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 485,439		$ 379,741
Percent of total commercial loans (percent)	2.00%		2.00%
Loans and Leases Receivable, Allowance	$ 10,585		$ 7,973
Commercial Loan P D Grade Twelve | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 224,788		$ 342,537
Percent of total commercial loans (percent)	1.00%		2.00%
Loans and Leases Receivable, Allowance	$ 5,945		$ 6,972
Commercial Loan P D Grade Thirteen | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan, disaggregated by PD grade	$ 271,579		$ 347,432
Percent of total commercial loans (percent)	1.00%		2.00%
Loans and Leases Receivable, Allowance	$ 8,726		$ 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	$ 246,916		$ 254,525
Percent of total commercial loans (percent)	1.00%		1.00%
Loans and Leases Receivable, Allowance	$ 22,546		$ 23,307
C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Allowance	116,096	103,713	98,947	96,834	100,238	98,211
Total loans collectively evaluated for impairment	18,904,621			16,349,811
Total loans individually evaluated for impairment	115,808			32,599
Purchased credit-impaired loans	33,840			56,335
Allowance - collectively evaluated for impairment	106,758			93,429
Allowance - individually evaluated for impairment	8,484			1,213
Allowance - purchased credit-impaired loans	854			2,192
C&I | General C&I | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans collectively evaluated for impairment	14,925,394		14,152,795
Total loans individually evaluated for impairment	75,778		45,704
Purchased credit-impaired loans	33,840		41,730
Total commercial loans	15,035,012		14,240,229
C&I | Loans to Mortgage Companies | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans collectively evaluated for impairment	3,751,656		2,023,746
Total loans individually evaluated for impairment	37,256		0
Purchased credit-impaired loans	0		0
Total commercial loans	3,788,912		2,023,746
C&I | TRUPs | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans collectively evaluated for impairment	227,571		247,465
Total loans individually evaluated for impairment	2,774		2,888
Purchased credit-impaired loans	0		0
Total commercial loans	230,345		250,353
Valuation allowance	19,100		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	644,320		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	784,770		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	714,521		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	1,005,546		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	1,323,078		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	783,813		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	35,786		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	2,039,017		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	625,650		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	80,765		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	2,372,435		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	762,708		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	2,788,867		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	215,894		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	1,435,796		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	234,238		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	1,235,046		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	111,728		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	26,123		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	555,544		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	7,218		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	414,018		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	12,000		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	196,321		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	4,861		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	213,551		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	208,110		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	32,953	$ 34,382	31,311	33,832	$ 29,057	$ 28,427
Total loans collectively evaluated for impairment	3,852,027			4,106,974
Total loans individually evaluated for impairment	1,777			2,252
Purchased credit-impaired loans	7,227			27,130
Allowance - collectively evaluated for impairment	32,953			33,744
Allowance - individually evaluated for impairment	0			0
Allowance - purchased credit-impaired loans	0			$ 88
Commercial real estate | Income CRE | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans collectively evaluated for impairment	3,731,807		3,877,848
Total loans individually evaluated for impairment	1,777		1,966
Purchased credit-impaired loans	5,722		12,730
Total commercial loans	3,739,306		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	120,220		135,893
Total loans individually evaluated for impairment	0		0
Purchased credit-impaired loans	1,505		2,433
Total commercial loans	121,725		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	12,771		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	7,498		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	22		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	381,343		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	715		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	392,617		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	425		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	946,927		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	20,306		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	661,250		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	12,940		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	588,840		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	37,809		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	258,834		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	22,247		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	229,873		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	14,096		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	85,578		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	3,861		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	55,898		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	3,523		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	22,436		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	1,170		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	50,113		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	2,129		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	37,829		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	$ 977		$ 837