Stockholders' Equity - Reclassifications from accumulated other comprehensive income (loss) and included in net income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassifications from accumulated other comprehensive income (loss)
Reclassifications included in net income:
Pre-tax	$ (1,050)	$ (937)	$ (2,154)	$ (2,714)
Tax (expense) benefit	429	566	894	1,184
Net of tax	(621)	(371)	(1,260)	(1,530)
Sponsored funds investment gains | Investment and other income (loss) | Reclassifications from accumulated other comprehensive income (loss)
Reclassifications included in net income:
Pre-tax	106	589	253	508
Tax (expense) benefit	(39)	(219)	(94)	(189)
Net of tax	67	370	159	319
Change in valuation allowance for unrealized gains (losses) on investment securities
Reclassifications included in net income:
Net of tax	39	219	94	188
Change in valuation allowance for unrealized gains (losses) on investment securities | Provision for income taxes | Reclassifications from accumulated other comprehensive income (loss)
Reclassifications included in net income:
Tax (expense) benefit	39	219	94	188
Net of tax	39	219	94	188
Pension and postretirement benefits
Reclassifications included in net income:
Net of tax	(727)	(960)	(1,513)	(2,037)
Pension and postretirement benefits | Underwriting and distribution expense and Compensation and related costs | Reclassifications from accumulated other comprehensive income (loss)
Reclassifications included in net income:
Pre-tax	(1,156)	(1,526)	(2,407)	(3,222)
Tax (expense) benefit	429	566	894	1,185
Net of tax	$ (727)	$ (960)	$ (1,513)	$ (2,037)