Stockholders' Equity - Reclassifications from accumulated other comprehensive income (loss) and included in net income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Reclassifications from accumulated other comprehensive income (loss)
Reclassifications included in net income:
Pre-tax	$ (23,637)	$ (4,804)
Tax (expense) benefit	10,066	2,042
Net of tax	(13,571)	(2,762)
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	3,489	850
Tax (expense) benefit	(1,298)	(312)
Net of tax	2,191	538
Change in valuation allowance for unrealized gains (losses) on investment securities
Reclassifications included in net income:
Net of tax	1,343	306
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	1,343	306
Net of tax	1,343	306
Pension and postretirement benefits
Reclassifications included in net income:
Net of tax	(17,105)	(3,606)
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	(27,126)	(5,654)
Tax (expense) benefit	10,021	2,048
Net of tax	$ (17,105)	$ (3,606)