Securities Available-For-Sale (Details) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) Integer	Dec. 31, 2016 USD ($) Integer
Investments, Debt and Equity Securities [Abstract]
Increase in amortized cost basis of available-for-sale securities	$ 210.0
Net increase to accumulated other comprehensive income net of tax	$ 7.4
Number of Investment Securities Sold | Integer		75	84
Available-for-sale Securities Pledged as Collateral		$ 139.5	$ 121.9
Description of Holding Securities		there were no holdings of securities of any one issuer, other than the U.S. Government and its agencies, in an amount greater than 10% of stockholders’ equity.	there were no holdings of securities of any one issuer, other than the U.S. Government and its agencies, in an amount greater than 10% of stockholders’ equity.