Fair Value Measurements Details of Book Value and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
AFS, at estimated fair value	$ 2,793,480	$ 2,497,537
HTM securities	324,940
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	1,534,890	517,791
FRB and FHLB stock	93,964	97,422
Loans held for sale	93,621	37,828
AFS, at estimated fair value	2,793,480	2,497,537
HTM securities	304,241	369,841
Net Loans	18,761,796	16,673,904
Accrued interest receivable	70,766	60,898
Other financial assets	694,442	431,565
Demand and savings deposits	17,997,443	14,327,453
Brokered deposits	317,588	264,531
Time deposits	2,415,020	2,801,930
Short-term borrowings	611,727	883,241
Accrued interest payable	9,123	8,834
Other financial liabilities	352,740	221,542
FHLB advances and long-term debt	1,296,012	881,769
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	1,534,890	517,791
FRB and FHLB stock	93,964	97,422
Loans held for sale	93,621	37,828
AFS, at estimated fair value	2,793,480	2,497,537
HTM securities	324,940	383,705
Net Loans	18,514,547	16,485,122
Accrued interest receivable	70,766	60,898
Other financial assets	694,442	431,565
Demand and savings deposits	17,997,443	14,327,453
Brokered deposits	317,588	264,531
Time deposits	2,442,422	2,828,988
Short-term borrowings	611,727	883,241
Accrued interest payable	9,123	8,834
Other financial liabilities	352,740	221,542
FHLB advances and long-term debt	1,342,192	878,385
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	1,534,890	517,791
FRB and FHLB stock	0	0
Loans held for sale	0	0
AFS, at estimated fair value	0	0
HTM securities	0	0
Net Loans	0	0
Accrued interest receivable	70,766	60,898
Other financial assets	272,632	234,176
Demand and savings deposits	17,997,443	14,327,453
Brokered deposits	275,719	223,982
Time deposits	0	0
Short-term borrowings	611,727	883,241
Accrued interest payable	9,123	8,834
Other financial liabilities	152,272	142,508
FHLB advances and long-term debt	0	0
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	0	0
FRB and FHLB stock	93,964	97,422
Loans held for sale	93,621	37,828
AFS, at estimated fair value	2,695,490	2,393,211
HTM securities	324,940	383,705
Net Loans	0	0
Accrued interest receivable	0	0
Other financial assets	387,563	145,365
Demand and savings deposits	0	0
Brokered deposits	41,869	40,549
Time deposits	2,442,422	2,828,988
Short-term borrowings	0	0
Accrued interest payable	0	0
Other financial liabilities	184,935	76,447
FHLB advances and long-term debt	1,342,192	878,385
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	0	0
FRB and FHLB stock	0	0
Loans held for sale	0	0
AFS, at estimated fair value	97,990	104,326
HTM securities	0	0
Net Loans	18,514,547	16,485,122
Accrued interest receivable	0	0
Other financial assets	34,247	52,024
Demand and savings deposits	0	0
Brokered deposits	0	0
Time deposits	0	0
Short-term borrowings	0	0
Accrued interest payable	0	0
Other financial liabilities	15,533	2,587
FHLB advances and long-term debt	$ 0	$ 0