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Summary of Significant Accounting Policies Narrative (Details)
$ in Thousands
 12 Months Ended
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Fully depreciated assets taken out of service $ 10,400 $ 7,400  
Deferred Sales Commission Asset B-Shares Estimated Period Of Benefit 8 years    
Amortization of deferred sales commissions $ 15,054 12,699 $ 9,153
Total Waived Fees 662,700 764,300 802,500
Change in Voluntary Yield-related Fee Waivers (77,000)    
Change due to competitive waivers (25,200)    
Advertising Expense $ 2,600 $ 2,200 $ 2,900
Number of operating segments 1    
Minimum [Member]      
Property and equipment, useful Life 1 year    
Finite-Lived Intangible Assets, Useful Life 8 years    
Maximum [Member]      
Property and equipment, useful Life 12 years    
Finite-Lived Intangible Assets, Useful Life 11 years    
Software and Software Development Costs [Member]      
Property and equipment, useful Life 4 years