Investment Securities (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Aug. 31, 2017	Dec. 31, 2016
Marketable investment securities—current, at fair value:
Total marketable investment securities - current	$ 485,035,000		$ 485,035,000			$ 522,516,000
Restricted marketable investment securities	12,961,000		12,961,000			12,203,000
Total	497,996,000		497,996,000			534,719,000
Restricted cash and cash equivalents	775,000		775,000			723,000
Other-than-temporary impairment loss on available-for-sale securities	0	$ 0	(3,298,000)	$ 0
Cost Method Investments	65,438,000		65,438,000			80,052,000
Privately Held Company
Marketable investment securities—current, at fair value:
Cost Method Investments					$ 4,100,000
Corporate bonds
Marketable investment securities—current, at fair value:
Marketable investment securities, at fair value	245,419,000		245,419,000			402,670,000
Strategic equity securities
Marketable investment securities—current, at fair value:
Marketable investment securities, at fair value	139,373,000		139,373,000			94,816,000
Other-than-temporary impairment loss on available-for-sale securities			(3,300,000)
Fair values of trading securities	23,900,000		23,900,000			7,200,000
Strategic equity securities | Other Nonoperating Income (Expense)
Marketable investment securities—current, at fair value:
Dividend income from strategic equity securities	2,300,000		5,800,000
Strategic equity securities | Gains on investments, net
Marketable investment securities—current, at fair value:
Gains (losses) related to trading securities	19,900,000	$ 0	19,900,000	$ (1,000,000.0)
Other
Marketable investment securities—current, at fair value:
Total marketable investment securities - current	$ 100,243,000		$ 100,243,000			$ 25,030,000