Fair Value Measurements - Changes in Level 3 Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Interest rate lock commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Beginning Balance	$ 2,375	[1],[2]	$ 0
Total Realized and Unrealized Gains (Losses), Assets	5,201	[2],[3],[4]	2,375	[3],[5]
Purchases and Issuances	0	[2],[6]
Sales and Settlements	0	[2]
Transfers In (Out)	0	[2]
Assets Ending Balance	7,576	[2]	2,375	[1],[2]
Liabilities Beginning Balance	3,653		0
Total Realized and Unrealized Gains (Loss), Liabilities	2,431	[3],[5]	(3,653)
Liabilities Ending Balance	1,222		3,653
Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Beginning Balance	5,946	[1],[7]	12,954	[1]
Total Realized and Unrealized Gains (Losses), Assets	101	[3],[4],[7]	929	[1],[3],[5]
Purchases and Issuances	5,178	[6],[7]	1,414	[1],[4]
Sales and Settlements	(1,097)	[7]	(8,898)	[1]
Transfers In (Out)	(620)	[7]	(453)	[1]
Assets Ending Balance	9,508	[7]	5,946	[1],[7]
Auction rate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Beginning Balance	85,124	[6],[8],[9]	72,118	[6],[8]
Total Realized and Unrealized Gains (Losses), Assets	(622)	[3],[4],[8],[9]	(1,409)	[3],[5],[6],[8]
Purchases and Issuances	20,625	[6],[8],[9]	21,875	[4],[6],[8]
Sales and Settlements	(13,705)	[8],[9]	(7,460)	[6],[8]
Transfers In (Out)	0	[8],[9]
Assets Ending Balance	91,422	[8],[9]	85,124	[6],[8],[9]
Liabilities Beginning Balance			100	[8]
Purchases and Issuances			100
Auction Rate Securities Purchase Commitment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities Beginning Balance	2,600	[5],[7]	2,647	[7]
Total Realized and Unrealized Gains (Loss), Liabilities	1,698	[3],[5],[7]	47	[3],[5],[7]
Liabilities Ending Balance	902	[5]	2,600	[5],[7]
Municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Beginning Balance	236		239
Total Realized and Unrealized Gains (Losses), Assets	(72)	[3],[4]	(3)	[3],[5]
Purchases and Issuances	0	[6]
Sales and Settlements	0
Transfers In (Out)	0
Assets Ending Balance	164		236
Mortgage and other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Beginning Balance			40	[10]
Sales and Settlements			(8)	[10]
Transfers In (Out)			$ (32)	[10]

[1] Interest rate lock commitment assets and liabilities are recorded upon the commitment to originate a loan with a borrower and sell the loan to an investor. The commitment assets and liabilities are recognized at fair value, which reflects the fair value of the contractual loan origination related fees and sale premiums, net of co-broker fees, and the estimated fair value of the expected net future cash flows associated with the servicing of the loan.

[2] Interest rate lock commitment assets and liabilities are recorded upon the commitment to originate a loan with a borrower and sell the loan to an investor. The commitment assets and liabilities are recognized at fair value, which reflects the fair value of the contractual loan origination related fees and sale premiums, net of co-broker fees, and the estimated fair value of the expected net future cash flows associated with the servicing of the loan

[3] Included in principal transactions on the consolidated statement of operations, except for investments which are included in other income on the consolidated statement of operations.

[4] Unrealized gains (losses) are attributable to assets or liabilities that are still held at the reporting date.

[5] Represents the difference in principal and fair value for auction rate securities purchase commitments outstanding at the end of the year.

[6] Purchases and issuances in connection with ARS purchase commitments represent instances in which the Company purchased ARS securities from clients during the period pursuant to regulatory and legal settlements and awards that satisfy the outstanding commitment to purchase obligation. This also includes instances where the ARS issuer has redeemed ARS where the Company had an outstanding purchase commitment prior to the Company purchasing those ARS.

[7] Primarily represents general partner ownership and limited partner interests in hedge funds and private equity funds sponsored by the Company.

[8] Represents auction rate preferred securities, municipal auction rate securities and student loan auction rate securities that failed in the auction rate market.

[9] Sales and settlements for the ARS purchase commitments represent additional purchase commitments made during the year for regulatory and legal ARS settlements and awards.

[10] Represents private placements of non-agency collateralized mortgage obligations.