Securities Owned and Securities Sold, But Not Yet Purchased - Additional Information (Details) (USD $) | Sep. 30, 2014 | Dec. 31, 2013 |
In Thousands, unless otherwise specified |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | $5,858 | $4,789 |
Securities sold, but not yet purchased | -3,434 | -83 |
Level 1 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 1,805 | 713 |
Securities sold, but not yet purchased | -3,071 | -33 |
Level 2 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 4,053 | 4,076 |
Securities sold, but not yet purchased | -363 | -50 |
Level 3 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 0 | 0 |
Securities sold, but not yet purchased | 0 | 0 |
Debt securities | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 1,896 | 1,402 |
Securities sold, but not yet purchased | -66 | -46 |
Debt securities | Level 1 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 0 | 0 |
Securities sold, but not yet purchased | ' | 0 |
Debt securities | Level 2 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 1,896 | 1,402 |
Securities sold, but not yet purchased | ' | -46 |
Debt securities | Level 3 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 0 | 0 |
Securities sold, but not yet purchased | ' | 0 |
Certificates of deposit | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | ' | 24 |
Securities sold, but not yet purchased | -66 | 0 |
Certificates of deposit | Level 1 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | ' | 24 |
Securities sold, but not yet purchased | 0 | ' |
Certificates of deposit | Level 2 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | ' | 0 |
Securities sold, but not yet purchased | -66 | ' |
Certificates of deposit | Level 3 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | ' | 0 |
Securities sold, but not yet purchased | 0 | ' |
U.S. Treasury notes | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 1 | 1 |
Securities sold, but not yet purchased | -297 | 0 |
U.S. Treasury notes | Level 1 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 0 | 0 |
Securities sold, but not yet purchased | 0 | ' |
U.S. Treasury notes | Level 2 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 1 | 1 |
Securities sold, but not yet purchased | -297 | ' |
U.S. Treasury notes | Level 3 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 0 | 0 |
Securities sold, but not yet purchased | 0 | ' |
Common stock and warrants | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 1,805 | 689 |
Securities sold, but not yet purchased | -3,071 | -33 |
Other investments | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 1,025 | 1,948 |
Securities sold, but not yet purchased | 0 | 0 |
Other investments | Level 1 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 0 | 0 |
Other investments | Level 2 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 1,025 | 1,948 |
Other investments | Level 3 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 0 | 0 |
Common stock, restricted common stock and warrants | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 2,936 | 1,414 |
Securities sold, but not yet purchased | -3,071 | -37 |
Common stock, restricted common stock and warrants | Level 1 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 1,805 | 689 |
Securities sold, but not yet purchased | -3,071 | -33 |
Common stock, restricted common stock and warrants | Level 2 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 1,131 | 725 |
Securities sold, but not yet purchased | 0 | -4 |
Common stock, restricted common stock and warrants | Level 3 | ' | ' |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] | ' | ' |
Securities owned at fair value | 0 | 0 |
Securities sold, but not yet purchased | $0 | $0 |