Fair Value Measurements Details of Book Value and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
AFS, at estimated fair value	$ 2,758,597	$ 3,062,143
HTM securities	843,743
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	1,661,876	1,847,832
FRB and FHLB stock	66,209	92,129
Loans held for sale	34,092	83,886
AFS, at estimated fair value	2,758,597	3,062,143
HTM securities	853,413	278,281
Net Loans	18,725,000	18,623,253
Accrued interest receivable	65,649	72,942
Other financial assets	510,534	650,425
Demand and savings deposits	19,250,538	18,279,358
Brokered deposits	309,873	335,185
Time deposits	2,073,427	2,224,665
Short-term borrowings	520,989	630,066
Accrued interest payable	5,618	10,365
Other financial liabilities	297,069	338,747
FHLB advances and long-term debt	626,407	1,296,263
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	1,661,876	1,847,832
FRB and FHLB stock	66,209	92,129
Loans held for sale	34,092	83,886
AFS, at estimated fair value	2,758,597	3,062,143
HTM securities	843,743	296,857
Net Loans	18,354,532	18,354,532
Accrued interest receivable	65,649	72,942
Other financial assets	510,534	650,425
Demand and savings deposits	19,250,538	18,279,358
Brokered deposits	310,874	336,391
Time deposits	2,087,663	2,246,457
Short-term borrowings	520,989	630,066
Accrued interest payable	5,618	10,365
Other financial liabilities	297,069	338,747
FHLB advances and long-term debt	607,577	1,332,041
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	1,661,876	1,847,832
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	65,649	72,942
Other financial assets	276,659	279,015
Demand and savings deposits	19,250,538	18,279,358
Brokered deposits	289,873	295,185
Time deposits	0	0
Short-term borrowings	520,989	630,066
Accrued interest payable	5,618	10,365
Other financial liabilities	173,899	156,869
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	66,209	92,129
Loans held for sale	34,092	83,886
AFS, at estimated fair value	2,682,393	2,963,937
HTM securities	843,743	296,857
Net Loans	0	0
Accrued interest receivable	0	0
Other financial assets	196,808	338,987
Demand and savings deposits	0	0
Brokered deposits	21,001	41,206
Time deposits	2,087,663	2,246,457
Short-term borrowings	0	0
Accrued interest payable	0	0
Other financial liabilities	108,897	167,505
FHLB advances and long-term debt	607,577	1,332,041
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	76,204	98,206
HTM securities	0	0
Net Loans	18,354,532	18,354,532
Accrued interest receivable	0	0
Other financial assets	37,067	32,423
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	14,273	14,373
FHLB advances and long-term debt	$ 0	$ 0