Investment Securities Available for Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 257,693	$ 254,837
Gross Unrealized Gains	88,855	94,801
Gross Unrealized Losses	(3,971)	(3,595)
Fair Value	342,577	346,043
Marketable equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost	71,275	63,041
Gross Unrealized Gains	88,746	92,244
Gross Unrealized Losses	(1,747)	(1,093)
Fair Value	158,274	154,192
Mutual funds invested in fixed income securities
Schedule of Available-for-sale Securities [Line Items]
Cost	62,399	61,485
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,958)	(1,659)
Fair Value	60,441	59,826
Marketable debt securities
Schedule of Available-for-sale Securities [Line Items]
Cost	124,019	130,311
Gross Unrealized Gains	109	2,557
Gross Unrealized Losses	(266)	(843)
Fair Value	$ 123,862	$ 132,025