Fair Value Measurements Details of Book Value and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
HTM securities	$ 354,109
Estimated Fair Value	2,644,299	$ 2,497,537
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	1,058,599	517,791
FRB and FHLB stock	91,042	97,422
Loans held for sale	77,415	37,828
HTM securities	330,514	369,841
Estimated Fair Value	2,644,299	2,497,537
Net Loans	18,448,185	16,673,904
Accrued interest receivable	73,720	60,898
Other financial assets	706,518	431,565
Demand and savings deposits	17,006,353	14,327,453
Brokered deposits	310,689	264,531
Time deposits	2,567,166	2,801,930
Short-term borrowings	572,551	883,241
Accrued interest payable	11,571	8,834
Other financial liabilities	369,624	221,542
FHLB advances and long-term debt	1,295,196	881,769
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	1,058,599	517,791
FRB and FHLB stock	91,042	97,422
Loans held for sale	77,415	37,828
HTM securities	354,109	383,705
Estimated Fair Value	2,644,299	2,497,537
Net Loans	18,173,117	16,485,122
Accrued interest receivable	73,720	60,898
Other financial assets	706,518	431,565
Demand and savings deposits	17,006,353	14,327,453
Brokered deposits	310,689	264,531
Time deposits	2,599,932	2,828,988
Short-term borrowings	572,551	883,241
Accrued interest payable	11,571	8,834
Other financial liabilities	369,624	221,542
FHLB advances and long-term debt	1,342,497	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	1,058,599	517,791
FRB and FHLB stock	0	0
Loans held for sale	0	0
HTM securities	0	0
Estimated Fair Value	0	0
Net Loans	0	0
Accrued interest receivable	73,720	60,898
Other financial assets	268,789	234,176
Demand and savings deposits	17,006,353	14,327,453
Brokered deposits	268,618	223,982
Time deposits	0	0
Short-term borrowings	572,551	883,241
Accrued interest payable	11,571	8,834
Other financial liabilities	162,614	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	91,042	97,422
Loans held for sale	77,415	37,828
HTM securities	354,109	383,705
Estimated Fair Value	2,543,440	2,393,211
Net Loans	0	0
Accrued interest receivable	0	0
Other financial assets	401,319	145,365
Demand and savings deposits	0	0
Brokered deposits	42,071	40,549
Time deposits	2,599,932	2,828,988
Short-term borrowings	0	0
Accrued interest payable	0	0
Other financial liabilities	190,627	76,447
FHLB advances and long-term debt	1,342,497	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
HTM securities	0	0
Estimated Fair Value	100,859	104,326
Net Loans	18,173,117	16,485,122
Accrued interest receivable	0	0
Other financial assets	36,410	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	16,383	2,587
FHLB advances and long-term debt	$ 0	$ 0