Basis of Presentation - Narrative (Details)	9 Months Ended
	Sep. 30, 2017 segment revenue_line
Segment Reporting, Revenue Reconciling Item [Line Items]
Number of reportable segments | segment	1
Number of revenue lines	5
Commissions, Fees and Other and Fiduciary Investment Income
Segment Reporting, Revenue Reconciling Item [Line Items]
Number of revenue lines	1