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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassifications included in net income:
Pre-tax	$ 233	$ (27)	$ 605	$ 1,329
Tax benefit (expense)	(56)	7	(144)	(455)
Net of tax	177	(20)	461	874
Sponsored funds investment losses | Retained earnings
Reclassifications included in net income:
Pre-tax				1,295
Tax benefit (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	109	(58)	234	(58)
Tax benefit (expense)	(26)	14	(56)	14
Net of tax	83	(44)	178	(44)
Postretirement benefits unrealized gains (losses) | Compensation and benefits
Reclassifications included in net income:
Pre-tax	124	31	371	92
Tax benefit (expense)	(30)	(7)	(88)	(129)
Net of tax	$ 94	$ 24	$ 283	$ (37)