Marketable Investment Securities, Restricted Cash and Cash Equivalents, and Other Investment Securities - Unrealized Gains (Losses) On Marketable Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accumulated net unrealized gains (losses)
Accumulated net unrealized gains, before tax, in accumulated other comprehensive income (loss)	$ (116)	$ 19,728
Accumulated net unrealized gains, net of tax, in accumulated other comprehensive income (loss)	1,000	12,000
Components of available-for-sale investments
Debt securities	3,833	141,335
Total marketable investment securities	85,512	223,615
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains	16	20,039
Unrealized Losses	(132)	(311)
Unrealized Gains Losses, Net	(116)	19,728
Contractual maturities of restricted and non-restricted marketable investment securities
Debt securities with contractual maturities within one year	51,000
Debt securities with contractual maturities extending longer than one year through and including five years	35,000
U.S. Treasury and agency securities
Accumulated net unrealized gains (losses)
Accumulated net unrealized gains, before tax, in accumulated other comprehensive income (loss)	(119)	(133)
Components of available-for-sale investments
Debt securities	81,982	82,124
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains	13	2
Unrealized Losses	(132)	(135)
Unrealized Gains Losses, Net	(119)	(133)
Corporate securities
Accumulated net unrealized gains (losses)
Accumulated net unrealized gains, before tax, in accumulated other comprehensive income (loss)	3	(171)
Components of available-for-sale investments
Debt securities	3,530	90,838
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains	3	3
Unrealized Losses		(174)
Unrealized Gains Losses, Net	$ 3	(171)
Other (including restricted)
Accumulated net unrealized gains (losses)
Accumulated net unrealized gains, before tax, in accumulated other comprehensive income (loss)		(2)
Components of available-for-sale investments
Debt securities		17,382
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Losses		(2)
Unrealized Gains Losses, Net		(2)
Equity Securities
Accumulated net unrealized gains (losses)
Accumulated net unrealized gains, before tax, in accumulated other comprehensive income (loss)		20,034
Components of available-for-sale investments
Equity securities		33,271
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains		20,034
Unrealized Gains Losses, Net		$ 20,034