Stockholders' Equity - Reclassifications from accumulated other comprehensive income (loss) and included in net income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reclassifications from accumulated other comprehensive income (loss)
Reclassifications included in net income:
Pre-tax	$ 1,369	$ (3,533)	$ (1,350)	$ (3,556)
Tax (expense) benefit	602	539	1,787	1,470
Net of tax	1,971	(2,994)	437	(2,086)
Realized loss on sale of sponsored investment securities | Investment and other income (loss) | Reclassifications from accumulated other comprehensive income (loss)
Reclassifications included in net income:
Pre-tax	2,980	(2,119)	3,483	685
Tax (expense) benefit	(1,109)	789	(1,296)	(251)
Net of tax	1,871	(1,330)	2,187	434
Change in valuation allowance for unrealized gains (losses) on investment securities
Reclassifications included in net income:
Net of tax	1,155	(776)	1,342	244
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	1,155	(776)	1,342	244
Net of tax	1,155	(776)	1,342	244
Pension and postretirement benefits
Reclassifications included in net income:
Net of tax	(1,055)	(888)	(3,092)	(2,764)
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	(1,611)	(1,414)	(4,833)	(4,241)
Tax (expense) benefit	556	526	1,741	1,477
Net of tax	$ (1,055)	$ (888)	$ (3,092)	$ (2,764)