Marketable Investment Securities, Restricted Cash and Cash Equivalents, and Other Investment Securities - Unrealized Gain (Losses) On Marketable Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Components of our available-for-sale investments
Debt securities	$ 291,862	$ 117,295
Debt securities	267,799	35,616
Equity security	47,856
Total marketable investment securities	339,718	117,295
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains	8,267	1,404
Unrealized Losses	(182)	(143)
Unrealized Gains Losses, Net	8,085	1,261
Contractual maturities of restricted and non-restricted marketable investment securities
Debt securities with contractual maturities within one year	271,000
Debt securities with contractual maturities extending longer than one year through and including five years	21,000
Accumulated net unrealized gains (losses)
Accumulated net unrealized gains, before tax, in accumulated other comprehensive income (loss)	8,000	1,000
Accumulated net unrealized gains, net of tax, in accumulated other comprehensive income (loss)	5,000	1,000
US Treasury and agency securities
Components of our available-for-sale investments
Debt securities	86,029	81,982
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains	1	13
Unrealized Losses	(133)	(132)
Unrealized Gains Losses, Net	(132)	(119)
Commercial paper
Components of our available-for-sale investments
Debt securities	27,843
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Losses	(1)
Unrealized Gains Losses, Net	(1)
Corporate securities
Components of our available-for-sale investments
Debt securities	175,393	33,555
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains	8,207	1,327
Unrealized Losses	(37)
Unrealized Gains Losses, Net	8,170	1,327
Other (including restricted)
Components of our available-for-sale investments
Debt securities	2,597	1,758
Unrealized Gains (Losses) on Marketable Investment Securities
Unrealized Gains	59	64
Unrealized Losses	(11)	(11)
Unrealized Gains Losses, Net	$ 48	$ 53