Investments in Equity Securities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 358,624	$ 308,175
Gross Unrealized, Gains	85,961	70,205
Gross Unrealized, Losses	(9,744)	(2,358)
Carrying and fair value of equity securities	434,841	376,022
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Cost	275,719	222,671
Gross Unrealized, Gains	60,277	60,102
Gross Unrealized, Losses	(5,360)	(707)
Carrying and fair value of equity securities	330,636	282,066
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Cost	82,905	85,504
Gross Unrealized, Gains	25,684	10,103
Gross Unrealized, Losses	(4,384)	(1,651)
Carrying and fair value of equity securities	$ 104,205	$ 93,956