Commitments and Contingencies Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 11, 2019
Loss Contingencies [Line Items]
Auction Rate Securities Committed To Purchase related to settlements with regulators	$ 7,000,000
SEC - SCSD Initiative Settlement Amount		$ 3,500,000
Minimum [Member]
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Portion Not Accrued	0
Eligible Investor Subject To Future Buyback Potential Additional Losses Related To Valuation Adjustments	0
Maximum [Member]
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Portion Not Accrued	21,000,000
Auction Rate Securities [Member]
Loss Contingencies [Line Items]
Amount Of Auction Rate Securities Firm Purchased And Hold	40,700,000
Auction Rate Securities Purchase Commitment [Member]
Loss Contingencies [Line Items]
Auction Rate Securities Committed To Purchase From Client	$ 7,400,000