Fair Value Measurements - Changes in Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) | Mar. 31, 2014 | Dec. 31, 2013 |
In Thousands, unless otherwise specified |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Cash equivalents | $234,181 | $270,262 |
Total assets measured at fair value | 332,429 | 303,450 |
Sponsored Mutual Funds and Variable Insurance Funds [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Marketable securities trading | 82,198 | 17,904 |
Equity Securities [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Marketable securities trading | 8,910 | 8,379 |
Sponsored Closed-End Funds [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Marketable securities available for sale | 2,841 | 2,685 |
Nonqualified Retirement Plan Assets [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Other investments, nonqualified retirement plan assets | 4,299 | 4,220 |
Level 1 [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Cash equivalents | 234,181 | 270,262 |
Total assets measured at fair value | 332,429 | 303,450 |
Level 1 [Member] | Sponsored Mutual Funds and Variable Insurance Funds [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Marketable securities trading | 82,198 | 17,904 |
Level 1 [Member] | Equity Securities [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Marketable securities trading | 8,910 | 8,379 |
Level 1 [Member] | Sponsored Closed-End Funds [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Marketable securities available for sale | 2,841 | 2,685 |
Level 1 [Member] | Nonqualified Retirement Plan Assets [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Other investments, nonqualified retirement plan assets | 4,299 | 4,220 |
Level 2 [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Cash equivalents | 0 | ' |
Total assets measured at fair value | 0 | ' |
Level 2 [Member] | Sponsored Mutual Funds and Variable Insurance Funds [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Marketable securities trading | 0 | ' |
Level 2 [Member] | Equity Securities [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Marketable securities trading | 0 | ' |
Level 2 [Member] | Sponsored Closed-End Funds [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Marketable securities available for sale | 0 | ' |
Level 2 [Member] | Nonqualified Retirement Plan Assets [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Other investments, nonqualified retirement plan assets | 0 | ' |
Level 3 [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Cash equivalents | 0 | ' |
Total assets measured at fair value | 0 | ' |
Level 3 [Member] | Sponsored Mutual Funds and Variable Insurance Funds [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Marketable securities trading | 0 | ' |
Level 3 [Member] | Equity Securities [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Marketable securities trading | 0 | ' |
Level 3 [Member] | Sponsored Closed-End Funds [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Marketable securities available for sale | 0 | ' |
Level 3 [Member] | Nonqualified Retirement Plan Assets [Member] | ' | ' |
Fair Value Inputs, Assets, Quantitative Information [Line Items] | ' | ' |
Other investments, nonqualified retirement plan assets | $0 | ' |