Investments in Qualified Affordable Housing Projects, Federal Historic Projects and New Market Tax Credits (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Variable Interest Entity [Line Items]
Expense related to qualified affordable housing projects	$ 1,000,000	$ 800,000
Remaining investment in qualified affordable housing projects	53,000,000		$ 51,400,000
Equity method investments	15,600,000		17,300,000
Remaining unfunded equity contributions	46,800,000		48,100,000
Investment tax credit	1,500,000
Impairment on tax credit projects	1,600,000		$ 0
Other Noninterest Expense [Member]
Variable Interest Entity [Line Items]
Impairment on tax credit projects	$ 1,300,000