Fair Value Measurements - Assets Accounted for at Fair Value on Recurring Basis (Detail) (USD $) | Dec. 31, 2013 | Dec. 31, 2012 |
In Thousands, unless otherwise specified |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | $474,315 | $469,747 |
Fair Value, Measurements, Recurring [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 474,315 | 469,747 |
Fair Value, Measurements, Recurring [Member] | Categories of Investments, Marketable Securities, Available-for-Sale Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 354,440 | ' |
Fair Value, Measurements, Recurring [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 89,346 |
Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 117,275 | 347,392 |
Fair Value, Measurements, Recurring [Member] | Restricted Cash and Cash Equivalents [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 2,600 | 33,009 |
Fair Value, Measurements, Recurring [Member] | U.S. Government Obligations and Agencies [Member] | Categories of Investments, Marketable Securities, Available-for-Sale Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 104,215 | ' |
Fair Value, Measurements, Recurring [Member] | U.S. Government Obligations and Agencies [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 4,009 |
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Categories of Investments, Marketable Securities, Available-for-Sale Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 94,203 | ' |
Fair Value, Measurements, Recurring [Member] | Mortgage-Backed and Asset-Backed Securities [Member] | Categories of Investments, Marketable Securities, Available-for-Sale Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 91,000 | ' |
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Categories of Investments, Marketable Securities, Available-for-Sale Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 9,295 | ' |
Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member] | Categories of Investments, Marketable Securities, Available-for-Sale Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 55,727 | ' |
Fair Value, Measurements, Recurring [Member] | Equity Securities, Common Stock, Metals and Mining [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 26,130 |
Fair Value, Measurements, Recurring [Member] | Equity Securities, Common Stock, Energy [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 10,868 |
Fair Value, Measurements, Recurring [Member] | Equity Securities, Common Stock, Other [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 8,215 |
Fair Value, Measurements, Recurring [Member] | Equity Securities, Exchange-Traded and Mutual Funds, Metals and Mining [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 21,989 |
Fair Value, Measurements, Recurring [Member] | Equity Securities, Exchange-Traded and Mutual Funds, Agriculture [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 10,265 |
Fair Value, Measurements, Recurring [Member] | Equity Securities, Exchange-Traded and Mutual Funds, Energy [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 5,068 |
Fair Value, Measurements, Recurring [Member] | Equity Securities, Exchange-Traded and Mutual Funds, Indices [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 2,506 |
Fair Value, Measurements, Recurring [Member] | Non-Hedging Derivate Liability, Net [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | -21 |
Fair Value, Measurements, Recurring [Member] | Other Investments [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 317 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 184,897 | 465,759 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Categories of Investments, Marketable Securities, Available-for-Sale Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 65,022 | ' |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 85,358 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 117,275 | 347,392 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Restricted Cash and Cash Equivalents [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 2,600 | 33,009 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Categories of Investments, Marketable Securities, Available-for-Sale Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 9,295 | ' |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member] | Categories of Investments, Marketable Securities, Available-for-Sale Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 55,727 | ' |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities, Common Stock, Metals and Mining [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 26,130 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities, Common Stock, Energy [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 10,868 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities, Common Stock, Other [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 8,215 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities, Exchange-Traded and Mutual Funds, Metals and Mining [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 21,989 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities, Exchange-Traded and Mutual Funds, Agriculture [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 10,265 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities, Exchange-Traded and Mutual Funds, Energy [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 5,068 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities, Exchange-Traded and Mutual Funds, Indices [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 2,506 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 317 |
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 289,418 | 3,988 |
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Categories of Investments, Marketable Securities, Available-for-Sale Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 289,418 | ' |
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 3,988 |
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Government Obligations and Agencies [Member] | Categories of Investments, Marketable Securities, Available-for-Sale Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 104,215 | ' |
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Government Obligations and Agencies [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | 4,009 |
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Categories of Investments, Marketable Securities, Available-for-Sale Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 94,203 | ' |
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-Backed and Asset-Backed Securities [Member] | Categories of Investments, Marketable Securities, Available-for-Sale Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | 91,000 | ' |
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Non-Hedging Derivate Liability, Net [Member] | Categories of Investments, Marketable Securities, Trading Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investment Owned, at Fair Value | ' | ($21) |