Investments - Cost and Fair Value of Available-For-Sale and Trading Investments Held (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Available-for-sale
Available-for-Sale, Amortized Cost	$ 1,975	$ 4,541
Available-for-Sale, Gross Unrealized Gains	12	1,644
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1,623	13
Available-for-Sale, Fair Value	364	6,172
Trading
Trading Securities, Amortized Cost	572,966	611,543
Trading Securities, Gross Unrealized Gains	2,621	21,016
Trading Securities, Gross Unrealized Losses	(35,679)	(26,726)
Trading Securities, Fair value	539,908	605,833
Proceeds from sales of available-for-sale investments	4,240	140	$ 10,884
Realized gains from sales of available-for-sale investments	1,300	0	4,700
Realized losses from sale of available-for-sale investments	0	0	$ 0
Equities [Member]
Available-for-sale
Equity Investments, Amortized Cost	1,778	4,339
Equity Investments, Gross Unrealized Gains	9	1,625
Equity Investments, Gross Unrealized Losses	(1,606)	(13)
Equity Investments, Fair Value	181	5,951
Trading
Trading Securities, Amortized Cost	357,844	411,898
Trading Securities, Gross Unrealized Gains	2,230	18,370
Trading Securities, Gross Unrealized Losses	(27,896)	(20,476)
Trading Securities, Fair value	332,178	409,792
Fixed Income Investments [Member]
Available-for-sale
Fixed Income Investments, Amortized Cost	197	202
Fixed Income Investments, Gross Unrealized Gains	3	19
Available-for-sale, Gross Unrealized Losses	(17)	0
Fixed Income Investments, Fair Value	183	221
Trading
Trading Securities, Amortized Cost	215,122	199,645
Trading Securities, Gross Unrealized Gains	391	2,646
Trading Securities, Gross Unrealized Losses	(7,783)	(6,250)
Trading Securities, Fair value	$ 207,730	$ 196,041