Fair Value Measurements - Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Total Fair Value Inputs [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Large Capitalization Registered Investment Companies	$ 338	$ 336
Mid Capitalization Registered Investment Companies	93	88
Small Capitalization Registered Investment Companies	76	72
International Developed And Emerging Markets Registered Investment Companies	179	187
Fixed Income Registered Investment Companies	45	48
Fixed General Account	161	173
Acquisition-related Consideration	5,010	4,901
Liabilities, Fair Value Disclosure	5,902	5,805
Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Large Capitalization Registered Investment Companies	338	336
Mid Capitalization Registered Investment Companies	93	88
Small Capitalization Registered Investment Companies	76	72
International Developed And Emerging Markets Registered Investment Companies	179	187
Fixed Income Registered Investment Companies	45	48
Fixed General Account	0	0
Acquisition-related Consideration	0	0
Liabilities, Fair Value Disclosure	731	731
Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Large Capitalization Registered Investment Companies	0	0
Mid Capitalization Registered Investment Companies	0	0
Small Capitalization Registered Investment Companies	0	0
International Developed And Emerging Markets Registered Investment Companies	0	0
Fixed Income Registered Investment Companies	0	0
Fixed General Account	161	173
Acquisition-related Consideration	0	0
Liabilities, Fair Value Disclosure	161	173
Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Large Capitalization Registered Investment Companies	0	0
Mid Capitalization Registered Investment Companies	0	0
Small Capitalization Registered Investment Companies	0	0
International Developed And Emerging Markets Registered Investment Companies	0	0
Fixed Income Registered Investment Companies	0	0
Fixed General Account	0	0
Acquisition-related Consideration	5,010	4,901
Liabilities, Fair Value Disclosure	$ 5,010	$ 4,901