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, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reclassifications from accumulated other comprehensive income (loss)
Reclassifications included in net income:
Pre-tax	$ (937)	$ (871)	$ (2,714)	$ (23)
Tax (expense) benefit	566	396	1,184	931
Net of tax	(371)	(475)	(1,530)	908
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	589	459	508	2,804
Tax (expense) benefit	(219)	(170)	(189)	(1,040)
Net of tax	370	289	319	1,764
Change in valuation allowance for unrealized gains (losses) on investment securities
Reclassifications included in net income:
Net of tax	219	169	188	1,020
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	219	169	188	1,020
Net of tax	219	169	188	1,020
Pension and postretirement benefits
Reclassifications included in net income:
Net of tax	(960)	(933)	(2,037)	(1,876)
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	(1,526)	(1,330)	(3,222)	(2,827)
Tax (expense) benefit	566	397	1,185	951
Net of tax	$ (960)	$ (933)	$ (2,037)	$ (1,876)