Investments - Cost and Fair Value of Available-For-Sale Investments Held (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of Investment Holdings [Line Items]
Available-for-Sale, Amortized Cost	$ 45	$ 385
Available-for-Sale, Gross Unrealized Gains	2	4
Available-for-sale, Gross Unrealized Losses	(2)	(25)
Available-for-Sale, Fair Value	45	364
Proceeds from sales of available-for-sale investments	372	4,240	$ 140
Realized gains from sales of available-for-sale investments		1,300	0
Realized losses from sale of available-for-sale investments	0	0	$ 0
Equities [Member]
Summary of Investment Holdings [Line Items]
Equity Investments, Amortized Cost	23	188
Equity Investments, Gross Unrealized Gains	0	2
Equity Investments, Gross Unrealized Losses	0	(9)
Equity Investments, Fair Value	23	181
Fixed Income Investments [Member]
Summary of Investment Holdings [Line Items]
Fixed Income Investments, Amortized Cost	22	197
Fixed Income Investments, Gross Unrealized Gains	2	2
Fixed income investments, Gross Unrealized Losses	(2)	(16)
Fixed Income Investments, Fair Value	$ 22	$ 183