Investment Securities (Other long-term investments) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Payments to Acquire Other Investments	$ 10,900	$ 6,500
Other Investments	321,800		$ 315,800
Hedge and private equity funds included in other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	131,300		127,800
Limited liability companies and private equity securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	84,700		82,100
Surplus Note
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	51,800		51,500
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	32,900		32,700
Affordable Housing Development Fund [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	14,100	$ 16,200	14,700	$ 16,800
Partnership investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	3,700		3,800
Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	3,300		3,200
Hedge Funds Equity R E I T [Member] | Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	20,200		20,600
Unfunded Commitments	$ 0		$ 0