Stockholders' Equity - Reclassifications from accumulated other comprehensive income (loss) and included in net income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassifications from accumulated other comprehensive income (loss)
Reclassifications included in net income:
Pre-tax	$ 1,325	$ 194
Tax (expense) benefit	(454)	(17)
Net of tax	871	177
Sponsored funds investment gains(losses) | Reclassifications from accumulated other comprehensive income (loss)
Reclassifications included in net income:
Pre-tax	1,295
Tax (expense) benefit	(340)
Net of tax	955
Sponsored funds investment gains(losses) | Investment and other income (loss) | Reclassifications from accumulated other comprehensive income (loss)
Reclassifications included in net income:
Pre-tax		148
Tax (expense) benefit		(56)
Net of tax		92
Change in valuation allowance for unrealized gains (losses) on investment securities
Reclassifications included in net income:
Net of tax		56
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		56
Net of tax		56
Postretirement benefits unrealized gains (losses)
Reclassifications included in net income:
Net of tax	23	29
Postretirement benefits unrealized gains (losses) | Compensation and benefits | Reclassifications from accumulated other comprehensive income (loss)
Reclassifications included in net income:
Pre-tax	30	46
Tax (expense) benefit	(114)	(17)
Net of tax	$ (84)	$ 29