Fair Value Measurements Financial Assets and Liabilities Measured on a Recurring and Nonrecurring Basis (Details) - USD ($) $ in Thousands | Jun. 30, 2015 | Dec. 31, 2014 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | $ 11,986 | $ 13,466 |
Securities sold, but not yet purchased | 1,735 | 302 |
Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents | 8,234 | 22,592 |
Securities owned — trading | 11,986 | 13,466 |
Other assets | 102,904 | 80,598 |
Total assets at fair value | 123,124 | 116,656 |
Securities sold, but not yet purchased | 1,735 | 302 |
Accounts payable and accrued liabilities | 527 | 527 |
Total liabilities at fair value | 2,262 | 829 |
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents | 8,234 | 22,592 |
Securities owned — trading | 11,965 | 12,087 |
Other assets | 98,804 | 75,540 |
Total assets at fair value | 119,003 | 110,219 |
Securities sold, but not yet purchased | 42 | 292 |
Accounts payable and accrued liabilities | 0 | 0 |
Total liabilities at fair value | 42 | 292 |
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents | 0 | 0 |
Securities owned — trading | 21 | 1,379 |
Other assets | 4,100 | 5,058 |
Total assets at fair value | 4,121 | 6,437 |
Securities sold, but not yet purchased | 1,693 | 10 |
Accounts payable and accrued liabilities | 0 | 0 |
Total liabilities at fair value | 1,693 | 10 |
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents | 0 | 0 |
Securities owned — trading | 0 | 0 |
Other assets | 0 | 0 |
Total assets at fair value | 0 | 0 |
Securities sold, but not yet purchased | 0 | 0 |
Accounts payable and accrued liabilities | 527 | 527 |
Total liabilities at fair value | 527 | 527 |
Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | | 13 |
Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | | 13 |
Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | | 0 |
Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | | 0 |
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 42 | 279 |
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 42 | 279 |
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 0 | 0 |
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 0 | 0 |
Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 1,693 | 10 |
Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 0 | 0 |
Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 1,693 | 10 |
Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities sold, but not yet purchased | 0 | 0 |
Money Market Funds [Member] | Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 262 | 293 |
Money Market Funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 262 | 293 |
Money Market Funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
Money Market Funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 7,333 | 7,570 |
Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 7,333 | 7,570 |
Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 60 | 224 |
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 60 | 224 |
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 21 | 1,379 |
Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 21 | 1,379 |
Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
U.S. treasury obligations | Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 4,310 | 4,000 |
U.S. treasury obligations | Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 4,310 | 4,000 |
U.S. treasury obligations | Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | 0 | 0 |
U.S. treasury obligations | Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Securities owned — trading | $ 0 | $ 0 |