Investments in Equity Securities Available for Sale (Investments in Equity Securities Available for Sale) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 220,587	$ 165,192
Gross Unrealized, Gains	453,298	8,216
Gross Unrealized, Losses	(4,685)	(22,542)
Carrying value and fair value of equity securities	669,200	150,866
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Cost	94,998	56,462
Gross Unrealized, Gains	351,906	0
Gross Unrealized, Losses	(1,046)	(19,189)
Carrying value and fair value of equity securities	445,858	37,273
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Cost	125,589	108,730
Gross Unrealized, Gains	101,392	8,216
Gross Unrealized, Losses	(3,639)	(3,353)
Carrying value and fair value of equity securities	$ 223,342	$ 113,593