Income Taxes Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Expense Components [Line Items]
Statutory Federal income tax rate	35.00%	35.00%	35.00%
Re-measurement of deferred tax assets and liabilities	13.70%	0.00%	0.00%
Nondeductible goodwill	10.10%	0.00%	0.00%
Tax-exempt interest, net	(10.30%)	(7.50%)	(7.10%)
State and local income tax, net of Federal tax benefit	6.90%	5.60%	5.50%
Tax credits	(3.10%)	(2.20%)	(1.90%)
Investments in affordable housing projects	2.20%	0.90%	0.90%
Noncontrolling interests	(1.50%)	(1.40%)	(1.60%)
Out-of-period adjustment	0.00%	0.00%	1.30%
Other, net	0.50%	0.20%	0.50%
Effective income tax rate	53.50%	30.60%	32.60%