Stockholders' Equity - Reclassifications from accumulated other comprehensive income (loss) and included in net income (Details) - Reclassifications from accumulated other comprehensive income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassifications included in net income:
Pre-tax	$ 249	$ 1,325
Tax expense	(60)	(454)
Net of tax	189	871
Sponsored funds investment losses | Retained earnings
Reclassifications included in net income:
Pre-tax		1,295
Tax expense		(340)
Net of tax		955
Gains (losses) on available for sale debt securities | Investment and other income (loss)
Reclassifications included in net income:
Pre-tax	125
Tax expense	(30)
Net of tax	95
Postretirement benefits unrealized gains (losses) | Compensation and benefits
Reclassifications included in net income:
Pre-tax	124	30
Tax expense	(30)	(114)
Net of tax	$ 94	$ (84)