Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Assets at Fair Value
Total financial instruments owned, at fair value	$ 479,232	$ 1,096,181
Loans held for sale, at fair value	7,693
Investments	21,597	20,478
Liabilities at Fair Value
Securities sold but not yet purchased	21,713	132,730
ClearPoint
Assets at Fair Value
Loans held for sale, at fair value	7,700
Level 1
Assets at Fair Value
Total financial instruments owned, at fair value	755	5,342
Total	755	5,342
Liabilities at Fair Value
Securities sold but not yet purchased	21,674
Total financial liabilities at fair value		130,210
Level 1 | Preferred stock
Assets at Fair Value
Total financial instruments owned, at fair value		2,439
Level 1 | U.S. government obligations
Assets at Fair Value
Total financial instruments owned, at fair value	25	1,996
Liabilities at Fair Value
Securities sold but not yet purchased	20,034	128,504
Level 1 | Equity securities
Assets at Fair Value
Total financial instruments owned, at fair value	730	675
Liabilities at Fair Value
Securities sold but not yet purchased		2
Level 1 | Derivatives
Assets at Fair Value
Total financial instruments owned, at fair value		232
Liabilities at Fair Value
Securities sold but not yet purchased	1,640	1,704
Level 2
Assets at Fair Value
Total financial instruments owned, at fair value	477,676	1,087,899
Total	485,369	1,087,899
Liabilities at Fair Value
Securities sold but not yet purchased	39
Total financial liabilities at fair value		2,520
Level 2 | ClearPoint
Assets at Fair Value
Loans held for sale, at fair value	7,693
Level 2 | Agency mortgage-backed securities
Assets at Fair Value
Total financial instruments owned, at fair value	462,940	903,928
Level 2 | Loans
Assets at Fair Value
Total financial instruments owned, at fair value		77,573
Level 2 | Federal agency obligations
Assets at Fair Value
Total financial instruments owned, at fair value	12,144	46,021
Level 2 | Corporate debt securities
Assets at Fair Value
Total financial instruments owned, at fair value	1,156	30,246
Liabilities at Fair Value
Securities sold but not yet purchased	39	2,520
Level 2 | Residential mortgage-backed securities
Assets at Fair Value
Total financial instruments owned, at fair value	438	23,077
Level 2 | Commercial mortgage-backed securities
Assets at Fair Value
Total financial instruments owned, at fair value		4,880
Level 2 | U.S. government obligations
Assets at Fair Value
Total financial instruments owned, at fair value		100
Level 2 | Other debt obligations
Assets at Fair Value
Total financial instruments owned, at fair value		2,074
Level 2 | Collateralized debt obligations
Assets at Fair Value
Total financial instruments owned, at fair value	998
Level 3
Assets at Fair Value
Total financial instruments owned, at fair value	801	2,940
Total	22,398	23,418
Level 3 | Agency mortgage-backed securities
Assets at Fair Value
Total financial instruments owned, at fair value	5	1,110
Level 3 | Residential mortgage-backed securities
Assets at Fair Value
Total financial instruments owned, at fair value	91	149
Level 3 | Commercial mortgage-backed securities
Assets at Fair Value
Total financial instruments owned, at fair value	18	18
Level 3 | Equity securities
Assets at Fair Value
Total financial instruments owned, at fair value	28	28
Level 3 | Collateralized debt obligations
Assets at Fair Value
Total financial instruments owned, at fair value	659	671
Level 3 | Derivatives
Assets at Fair Value
Total financial instruments owned, at fair value		964
Level 3 | Investments
Assets at Fair Value
Investments	21,597	20,478
Total
Assets at Fair Value
Total financial instruments owned, at fair value	479,232	1,096,181
Total	508,522	1,116,659
Liabilities at Fair Value
Securities sold but not yet purchased	21,713
Total financial liabilities at fair value		132,730
Total | ClearPoint
Assets at Fair Value
Loans held for sale, at fair value	7,693
Total | Agency mortgage-backed securities
Assets at Fair Value
Total financial instruments owned, at fair value	462,945	905,038
Total | Loans
Assets at Fair Value
Total financial instruments owned, at fair value		77,573
Total | Federal agency obligations
Assets at Fair Value
Total financial instruments owned, at fair value	12,144	46,021
Total | Corporate debt securities
Assets at Fair Value
Total financial instruments owned, at fair value	1,156	30,246
Liabilities at Fair Value
Securities sold but not yet purchased	39	2,520
Total | Residential mortgage-backed securities
Assets at Fair Value
Total financial instruments owned, at fair value	529	23,226
Total | Commercial mortgage-backed securities
Assets at Fair Value
Total financial instruments owned, at fair value	18	4,898
Total | Preferred stock
Assets at Fair Value
Total financial instruments owned, at fair value		2,439
Total | U.S. government obligations
Assets at Fair Value
Total financial instruments owned, at fair value	25	2,096
Liabilities at Fair Value
Securities sold but not yet purchased	20,034	128,504
Total | Other debt obligations
Assets at Fair Value
Total financial instruments owned, at fair value		2,074
Total | Equity securities
Assets at Fair Value
Total financial instruments owned, at fair value	758	703
Liabilities at Fair Value
Securities sold but not yet purchased		2
Total | Collateralized debt obligations
Assets at Fair Value
Total financial instruments owned, at fair value	1,657	671
Total | Derivatives
Assets at Fair Value
Total financial instruments owned, at fair value		1,196
Liabilities at Fair Value
Securities sold but not yet purchased	1,640	1,704
Total | Investments
Assets at Fair Value
Investments	$ 21,597	$ 20,478