Fair Value Measurements Details of Book Value and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
AFS, at estimated fair value	$ 3,062,143	$ 2,497,537
HTM securities	296,857
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	1,847,832	517,791
FRB and FHLB stock	92,129	97,422
Loans held for sale	83,886	37,828
AFS, at estimated fair value	278,281	369,841
HTM securities	3,062,143	2,497,537
Net Loans	18,623,253	16,673,904
Accrued interest receivable	72,942	60,898
Other financial assets	650,425	431,565
Demand and savings deposits	18,279,358	14,327,453
Brokered deposits	335,185	264,531
Time deposits	2,224,664	2,801,930
Short-term borrowings	10,365	8,834
Accrued interest payable	630,066	883,241
Other financial liabilities	338,747	221,542
FHLB advances and long-term debt	1,296,263	881,769
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	92,129	97,422
Loans held for sale	83,886	37,828
AFS, at estimated fair value	296,857	383,705
HTM securities	2,963,937	2,393,211
Net Loans	0	0
Accrued interest receivable	0	0
Other financial assets	338,987	145,365
Demand and savings deposits	0	0
Brokered deposits	41,206	40,549
Time deposits	2,246,457	2,828,988
Short-term borrowings	0	0
Accrued interest payable	0	0
Other financial liabilities	167,505	76,447
FHLB advances and long-term debt	1,332,041	878,385
Level 1 | 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	0	0
HTM securities	98,206	104,326
Net Loans	18,354,532	16,485,122
Accrued interest receivable	0	0
Other financial assets	32,423	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	14,373	2,587
FHLB advances and long-term debt	0	0
Level 2 | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	1,847,832	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	72,942	60,898
Other financial assets	279,015	234,176
Demand and savings deposits	18,279,358	14,327,453
Brokered deposits	295,185	224,531
Time deposits	0	0
Short-term borrowings	10,365	8,834
Accrued interest payable	630,066	883,241
Other financial liabilities	156,869	142,508
FHLB advances and long-term debt	0	0
Level 3 | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	1,847,832	517,791
FRB and FHLB stock	92,129	97,422
Loans held for sale	83,886	37,828
AFS, at estimated fair value	296,857	383,705
HTM securities	3,062,143	2,497,537
Net Loans	18,354,532	16,485,122
Accrued interest receivable	72,942	60,898
Other financial assets	650,425	431,565
Demand and savings deposits	18,279,358	14,327,453
Brokered deposits	336,391	265,080
Time deposits	2,246,457	2,828,988
Short-term borrowings	10,365	8,834
Accrued interest payable	630,066	883,241
Other financial liabilities	338,747	221,542
FHLB advances and long-term debt	$ 1,332,041	$ 878,385