Commitments and Contingencies - Additional Information (Narrative) (Details) - USD ($)						12 Months Ended
	Jan. 27, 2017	Nov. 30, 2016	Feb. 17, 2015	Feb. 09, 2015	Jan. 27, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Loss Contingencies [Line Items]
Operating leases expiring at various dates through						2028
Rent expense						$ 44,400,000	$ 45,900,000	$ 45,600,000
Capital Commitments Relating To Investments						1,300,000
Purchase Commitments Outstanding, Auction Rate Securities Related to Settlements with Regulators						5,000,000
Eligible investor subject to future buyback principal value						33,400,000
Auction rate securities
Loss Contingencies [Line Items]
Total amount of ARS the firm purchased and hold						88,100,000
Amount of ARS committed to purchase from clients						26,000,000
SEC
Loss Contingencies [Line Items]
Litigation Settlement, Amount					$ (10,000,000)
Payments for Legal Settlements			$ 5,000,000
SEC | Unfavorable Regulatory Action, Disgorgement
Loss Contingencies [Line Items]
Litigation Settlement, Amount					(4,200,000)
SEC | Unfavorable Regulatory Action, Prejudgment Interest
Loss Contingencies [Line Items]
Litigation Settlement, Amount					(753,500)
SEC | Unfavorable Regulatory Action, Civil Penalties
Loss Contingencies [Line Items]
Litigation Settlement, Amount					(5,100,000)
United States Department of the Treasury
Loss Contingencies [Line Items]
Litigation Settlement, Amount					$ (10,000,000)
Payments for Legal Settlements				$ 5,000,000
FINRA [Member]
Loss Contingencies [Line Items]
Payments for Legal Settlements		$ 1,600,000
Payments for Legal Settlements, Restitution to Eligible Clients		$ 1,800,000
Minimum [Member]
Loss Contingencies [Line Items]
Maximum estimated range of aggregate loss for legal proceedings						0
Eligible investor subject to future buyback potential additional losses related to valuation adjustments						0
Maximum [Member]
Loss Contingencies [Line Items]
Maximum estimated range of aggregate loss for legal proceedings						$ 47,000,000
Scenario, Forecast [Member] | SEC
Loss Contingencies [Line Items]
Payments for Legal Settlements	$ 5,000,000
Scenario, Forecast [Member] | United States Department of the Treasury
Loss Contingencies [Line Items]
Payments for Legal Settlements	$ 5,000,000