Federal Home Loan Bank and Federal Reserve Bank Borrowings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Federal Home Loan Bank, Advances, Maturities Summary, Average Interest Rate of Amounts Due within One Year of Balance Sheet Date	2.58%
Federal Home Loan Bank, Advances, Maturities Summary, Fixed Rate, under One Year	$ 4,000
FHLB Fixed Rate Advances, Maturities Summary [Abstract]
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	11,000
Valuation adjustment from acquisition accounting	579
FHLB Fixed Rate Advances, Total Amount	11,579
Federal Home Loan Bank, Advances, Activity for Year [Abstract]
FHLB Advances	11,579	$ 6,493	$ 68,531
Average balance during the year	79,788	79,673	70,678
Maximum month-end balance during the year	$ 317,480	$ 250,515	$ 242,556
Weighted average rate during the year	1.33%	0.80%	0.68%
Weighted average rate at December 31	4.08%	5.42%	0.79%
FHLB Advances, Collateral Pledged	$ 1,443,554	$ 1,510,514
FHLB Borrowing Capacity	1,432,554	1,502,284
Federal Reserve Bank, Advances, Activity for Year [Abstract]
Federal Reserve Bank, Advances, Collateral Pledged	100,054	61,007
Federal Reserve Bank borrowing capacity	100,054	61,007
Securities Investment [Member]
Federal Reserve Bank, Advances, Activity for Year [Abstract]
Federal Reserve Bank, Advances, Collateral Pledged	51,172	32,795
Loans Receivable [Member]
Federal Home Loan Bank, Advances, Activity for Year [Abstract]
FHLB Advances, Collateral Pledged	1,443,554	1,510,514
Commercial Loan [Member]
Federal Reserve Bank, Advances, Activity for Year [Abstract]
Federal Reserve Bank, Advances, Collateral Pledged	$ 48,882	$ 28,212