Federal Home Loan Bank and Federal Reserve Bank Borrowings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
FHLB Fixed Rate Advances, Maturities Summary [Abstract]
Federal Home Loan Bank, Advances, Maturities Summary, Average Interest Rate of Amounts Due within One Year of Balance Sheet Date	1.82%
Federal Home Loan Bank, Advances, Maturities Summary, Fixed Rate, under One Year	$ 946,000
Federal Home Loan Bank, Advances, Maturities Summary, Average Interest Rate, One To Five Years From Balance Sheet Date	3.85%
FHLB Fixed Rate Advances, Over 1 through 5 years	$ 2,000
FHLB Fixed Rate Advances, Weighted Average Interest Rate, Due after 10 years	5.37%
FHLB Fixed Rate Advances, Due after 10 years	$ 5,000
FHLB Fixed Rate Advances, Total Amount before valuation adjustment	953,000	$ 399,000
Valuation adjustment from acquisition accounting	469
FHLB Fixed Rate Advances, Total Amount	953,469
Federal Home Loan Bank, Advances, Activity for Year [Abstract]
FHLB Advances	953,469	399,523	$ 11,579
Federal Home Loan Bank, Advances, Activity for Year, Average Balance of Agreements Outstanding	469,983	166,563	79,788
Maximum month-end balance during the year	$ 953,469	$ 399,523	$ 317,480
Weighted average rate during the year	2.42%	2.29%	1.33%
Weighted average rate at December 31	1.84%	2.68%	4.08%
FHLB Borrowing Capacity	$ 1,960,000	$ 1,620,000
Federal Reserve Bank, Advances, Activity for Year [Abstract]
Average balance during the year	99	14
Federal Reserve Bank borrowing capacity	$ 209,100	$ 107,100