Qualified Affordable Housing Projects (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Investments in Affordable Housing Projects [Abstract]
Investment in qualified affordable housing projects	$ 6.7		$ 6.7		$ 8.7
Amortization expense included in noninterest expense	0.7	$ 0.8	2.0	$ 2.3
Tax credits	$ 0.8	$ 0.9	$ 2.3	$ 2.6