Fair Value Measurements Details of Book Value and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
HTM securities	$ 372,273
Estimated Fair Value	2,790,834	$ 2,497,537
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	856,360	517,791
FRB and FHLB stock	118,989	97,422
Loans held for sale	40,645	37,828
HTM securities	350,606	369,841
Estimated Fair Value	2,790,834	2,497,537
Net Loans	16,838,895	16,673,904
Accrued interest receivable	59,365	60,898
Other financial assets	658,025	431,565
Demand and savings deposits	14,349,257	14,327,453
Brokered deposits	313,337	264,531
Time deposits	2,702,432	2,801,930
Short-term borrowings	1,386,808	883,241
Accrued interest payable	10,890	8,834
Other financial liabilities	343,602	221,542
FHLB advances and long-term debt	1,378,466	881,769
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	856,360	517,791
FRB and FHLB stock	118,989	97,422
Loans held for sale	40,645	37,828
HTM securities	372,273	383,705
Estimated Fair Value	2,790,834	2,497,537
Net Loans	16,427,379	16,485,122
Accrued interest receivable	59,365	60,898
Other financial assets	658,025	431,565
Demand and savings deposits	14,349,257	14,327,453
Brokered deposits	313,337	264,531
Time deposits	2,730,425	2,828,988
Short-term borrowings	1,386,808	883,241
Accrued interest payable	10,890	8,834
Other financial liabilities	343,602	221,542
FHLB advances and long-term debt	1,421,214	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	856,360	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	59,365	60,898
Other financial assets	239,371	234,176
Demand and savings deposits	14,349,257	14,327,453
Brokered deposits	273,043	223,982
Time deposits	0	0
Short-term borrowings	1,386,808	883,241
Accrued interest payable	10,890	8,834
Other financial liabilities	139,868	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	118,989	97,422
Loans held for sale	40,645	37,828
HTM securities	372,273	383,705
Estimated Fair Value	2,695,008	2,393,211
Net Loans	0	0
Accrued interest receivable	0	0
Other financial assets	374,167	145,365
Demand and savings deposits	0	0
Brokered deposits	40,294	40,549
Time deposits	2,730,425	2,828,988
Short-term borrowings	0	0
Accrued interest payable	0	0
Other financial liabilities	184,771	76,447
FHLB advances and long-term debt	1,421,214	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	95,826	104,326
Net Loans	16,427,379	16,485,122
Accrued interest receivable	0	0
Other financial assets	44,487	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	18,963	2,587
FHLB advances and long-term debt	$ 0	$ 0