Fair Value Measurements - Changes in Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cash equivalents	$ 270,262	$ 62,289
Total assets measured at fair value	303,450	80,307
Sponsored Mutual Funds and Variable Insurance Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Marketable securities trading	17,904	8,013
Equity Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Marketable securities trading	8,379	4,379
Sponsored Closed-End Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Marketable securities available for sale	2,685	2,656
Nonqualified Retirement Plan Assets [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other investments, nonqualified retirement plan assets	4,220	2,970
Level 1 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cash equivalents	270,262	62,289
Total assets measured at fair value	303,450	80,307
Level 1 [Member] | Sponsored Mutual Funds and Variable Insurance Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Marketable securities trading	17,904	8,013
Level 1 [Member] | Equity Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Marketable securities trading	8,379	4,379
Level 1 [Member] | Sponsored Closed-End Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Marketable securities available for sale	2,685	2,656
Level 1 [Member] | Nonqualified Retirement Plan Assets [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other investments, nonqualified retirement plan assets	4,220	2,970
Level 2 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cash equivalents
Total assets measured at fair value
Level 2 [Member] | Sponsored Mutual Funds and Variable Insurance Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Marketable securities trading
Level 2 [Member] | Equity Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Marketable securities trading
Level 2 [Member] | Sponsored Closed-End Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Marketable securities available for sale
Level 2 [Member] | Nonqualified Retirement Plan Assets [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other investments, nonqualified retirement plan assets
Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Cash equivalents
Total assets measured at fair value
Level 3 [Member] | Sponsored Mutual Funds and Variable Insurance Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Marketable securities trading
Level 3 [Member] | Equity Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Marketable securities trading
Level 3 [Member] | Sponsored Closed-End Funds [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Marketable securities available for sale
Level 3 [Member] | Nonqualified Retirement Plan Assets [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other investments, nonqualified retirement plan assets