Fair Value Measurements Details of Book Value and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
AFS, at estimated fair value	$ 3,097,375	$ 3,062,143
HTM securities	826,932
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	1,904,059	1,847,832
FRB and FHLB stock	62,631	92,129
Loans held for sale	41,924	83,886
AFS, at estimated fair value	3,097,375	3,062,143
HTM securities	824,283	278,281
Net Loans	18,331,724	18,623,253
Accrued interest receivable	63,232	72,942
Other financial assets	542,967	650,425
Demand and savings deposits	19,514,090	18,279,358
Brokered deposits	277,444	335,185
Time deposits	1,932,778	2,224,664
Short-term borrowings	533,749	630,066
Accrued interest payable	7,322	10,365
Other financial liabilities	312,700	338,747
FHLB advances and long-term debt	627,213	1,296,263
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	1,904,059	1,847,832
FRB and FHLB stock	62,631	92,129
Loans held for sale	41,924	83,886
AFS, at estimated fair value	3,097,375	3,062,143
HTM securities	826,932	296,857
Net Loans	17,963,518	18,354,532
Accrued interest receivable	63,232	72,942
Other financial assets	542,967	650,425
Demand and savings deposits	19,514,090	18,279,358
Brokered deposits	278,274	336,391
Time deposits	1,942,321	2,246,457
Short-term borrowings	533,749	630,066
Accrued interest payable	7,322	10,365
Other financial liabilities	312,700	338,747
FHLB advances and long-term debt	617,167	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	1,904,059	1,847,832
FRB and FHLB stock	0	0
Loans held for sale	0	0
AFS, at estimated fair value	153,545	0
HTM securities	0	0
Net Loans	0	0
Accrued interest receivable	63,232	72,942
Other financial assets	295,025	279,015
Demand and savings deposits	19,514,090	18,279,358
Brokered deposits	257,444	295,185
Time deposits	0	0
Short-term borrowings	533,749	630,066
Accrued interest payable	7,322	10,365
Other financial liabilities	190,522	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	62,631	92,129
Loans held for sale	41,924	83,886
AFS, at estimated fair value	2,868,996	2,963,937
HTM securities	826,932	296,857
Net Loans	0	0
Accrued interest receivable	0	0
Other financial assets	215,701	338,987
Demand and savings deposits	0	0
Brokered deposits	20,830	41,206
Time deposits	1,942,321	2,246,457
Short-term borrowings	0	0
Accrued interest payable	0	0
Other financial liabilities	107,405	167,505
FHLB advances and long-term debt	617,167	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	74,834	98,206
HTM securities	0	0
Net Loans	17,963,518	18,354,532
Accrued interest receivable	0	0
Other financial assets	32,241	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	14,773	14,373
FHLB advances and long-term debt	$ 0	$ 0