Past Due Loans, Allowance For Credit Losses, Non-Accrual Loans, and TDRS - Loans and Related Allowance for Credit Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans, Individually Evaluated for Impairment	$ 84,059			$ 64,321
Loans, Collectively Evaluated for Impairment	14,328,750			12,608,826
Total	14,653,188			12,840,330
Allowance for Credit Losses Individually Evaluated for Impairment	7,650			3,992
Allowance for Credit Losses Collectively Evaluated for Impairment	202,338			102,033
Total Allowance for Credit Losses	246,873	$ 247,677	$ 76,000	109,222	$ 110,228	$ 106,929	$ 103,419
PCD
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	240,379			167,183
Total Allowance for Credit Losses	36,885		$ 35,700	3,197
Commercial industrial and agricultural
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans, Individually Evaluated for Impairment	51,289			34,142
Loans, Collectively Evaluated for Impairment	4,875,613			4,807,114
Total	5,013,037			4,887,141
Allowance for Credit Losses Individually Evaluated for Impairment	6,457			3,414
Allowance for Credit Losses Collectively Evaluated for Impairment	105,378			59,108
Total Allowance for Credit Losses	125,728	123,977		62,830	65,395	66,364	63,276
Commercial industrial and agricultural | PCD
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	86,135			45,885
Total Allowance for Credit Losses	13,893			308
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans, Individually Evaluated for Impairment	32,747			30,179
Loans, Collectively Evaluated for Impairment	4,740,442			4,552,796
Total	4,903,300			4,682,072
Allowance for Credit Losses Individually Evaluated for Impairment	1,193			578
Allowance for Credit Losses Collectively Evaluated for Impairment	37,441			16,301
Total Allowance for Credit Losses	60,840			18,635
Commercial real estate | PCD
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	130,111			99,097
Total Allowance for Credit Losses	22,206			1,756
Total corporate loans, excluding PPP loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans, Individually Evaluated for Impairment	84,036
Loans, Collectively Evaluated for Impairment	9,616,055
Total	9,916,337			9,569,213
Allowance for Credit Losses Individually Evaluated for Impairment	7,650
Allowance for Credit Losses Collectively Evaluated for Impairment	142,819
Total Allowance for Credit Losses	186,568
Total corporate loans, excluding PPP loans | PCD
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	216,246
Total Allowance for Credit Losses	36,099
PPP loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans, Individually Evaluated for Impairment	0
Loans, Collectively Evaluated for Impairment	1,196,538
Total	1,196,538			0
Allowance for Credit Losses Individually Evaluated for Impairment	0
Allowance for Credit Losses Collectively Evaluated for Impairment	0
Total Allowance for Credit Losses	0
PPP loans | PCD
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	0
Total Allowance for Credit Losses	0
Total corporate loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans, Individually Evaluated for Impairment	84,036			64,321
Loans, Collectively Evaluated for Impairment	10,812,593			9,359,910
Total	11,112,875			9,569,213
Allowance for Credit Losses Individually Evaluated for Impairment	7,650			3,992
Allowance for Credit Losses Collectively Evaluated for Impairment	142,819			75,409
Total Allowance for Credit Losses	186,568			81,465
Total corporate loans | PCD
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	216,246			144,982
Total Allowance for Credit Losses	36,099			2,064
Consumer loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans, Individually Evaluated for Impairment	23			0
Loans, Collectively Evaluated for Impairment	3,516,157			3,248,916
Total	3,540,313			3,271,117
Allowance for Credit Losses Individually Evaluated for Impairment	0			0
Allowance for Credit Losses Collectively Evaluated for Impairment	51,694			25,424
Total Allowance for Credit Losses	52,480			26,557
Consumer loans | PCD
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	24,133			22,201
Total Allowance for Credit Losses	786			1,133
Office, retail, and industrial | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans, Individually Evaluated for Impairment	25,345			24,820
Loans, Collectively Evaluated for Impairment	1,875,811			1,795,557
Total	1,950,406			1,848,718
Allowance for Credit Losses Individually Evaluated for Impairment	1,105			578
Allowance for Credit Losses Collectively Evaluated for Impairment	15,207			6,899
Total Allowance for Credit Losses	24,738	24,441		7,580	7,341	7,495	7,900
Office, retail, and industrial | Commercial real estate | PCD
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	49,250			28,341
Total Allowance for Credit Losses	8,426			103
Multi-family | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans, Individually Evaluated for Impairment	1,280			1,995
Loans, Collectively Evaluated for Impairment	860,002			851,857
Total	868,293			856,553
Allowance for Credit Losses Individually Evaluated for Impairment	0			0
Allowance for Credit Losses Collectively Evaluated for Impairment	5,465			2,854
Total Allowance for Credit Losses	5,739	5,311		2,950	2,762	2,159	2,464
Multi-family | Commercial real estate | PCD
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	7,011			2,701
Total Allowance for Credit Losses	274			96
Construction | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans, Individually Evaluated for Impairment	2,977			123
Loans, Collectively Evaluated for Impairment	612,681			581,747
Total	631,607			593,093
Allowance for Credit Losses Individually Evaluated for Impairment	0			0
Allowance for Credit Losses Collectively Evaluated for Impairment	4,722			1,681
Total Allowance for Credit Losses	6,732	11,522		1,697	1,766	1,862	2,173
Construction | Commercial real estate | PCD
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	15,949			11,223
Total Allowance for Credit Losses	2,010			16
Other commercial real estate | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans, Individually Evaluated for Impairment	3,145			3,241
Loans, Collectively Evaluated for Impairment	1,391,948			1,323,635
Total	1,452,994			1,383,708
Allowance for Credit Losses Individually Evaluated for Impairment	88			0
Allowance for Credit Losses Collectively Evaluated for Impairment	12,047			4,867
Total Allowance for Credit Losses	23,631	21,862		6,408	6,228	4,997	4,934
Other commercial real estate | Commercial real estate | PCD
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	57,901			56,832
Total Allowance for Credit Losses	11,496			1,541
Allowance for unfunded commitments
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans, Individually Evaluated for Impairment	0			0
Loans, Collectively Evaluated for Impairment	0			0
Total	0			0
Allowance for Credit Losses Individually Evaluated for Impairment	0			0
Allowance for Credit Losses Collectively Evaluated for Impairment	7,825			1,200
Total Allowance for Credit Losses	7,825	$ 7,625		1,200	$ 1,200	$ 1,200	$ 1,200
Allowance for unfunded commitments | PCD
Financing Receivable, Allowance for Credit Loss [Line Items]
Total	0			0
Total Allowance for Credit Losses	$ 0			$ 0