4. Cash, Cash Equivalents, and Marketable Securities (Details) - Available For Sale - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	$ 794,020	$ 705,900
Available-for-sale securities, gross unrealized gains	840	9
Available-for-sale securities, gross unrealized losses	640	2,455
Available-for-sale securities, estimated fair value	794,220	703,454
Available-for-sale securities, accumulated unrealized gain (loss)	200	(2,400)
Marketable securities, continuous unrealized loss position:
Available-for-sale securities, in loss position for less than 12 months, estimated fair value	352,151	629,033
Available-for-sale securities, continuous unrealized loss position, less than 12 months, accumulated loss	536	2,386
Available-for-sale securities, in loss position for 12 months or greater, estimated fair value	60,325	31,491
Available-for-sale securities, continuous unrealized loss position, 12 months or greater, accumulated loss	104	69
Available-for-sale securities, in loss position, estimated fair value	412,476	660,524
Available-for-sale securities, continuous unrealized loss position, accumulated loss	640	2,455
One year or less [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	291,072	290,377
Available-for-sale securities, gross unrealized gains	23	9
Available-for-sale securities, gross unrealized losses	134	406
Available-for-sale securities, estimated fair value	290,961	289,980
One year to two years [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	238,008	228,492
Available-for-sale securities, gross unrealized gains	104	0
Available-for-sale securities, gross unrealized losses	365	1,183
Available-for-sale securities, estimated fair value	237,747	227,309
Two years to three years [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	264,940	187,031
Available-for-sale securities, gross unrealized gains	713	0
Available-for-sale securities, gross unrealized losses	141	866
Available-for-sale securities, estimated fair value	265,512	186,165
Foreign debt [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	754,020	665,900
Available-for-sale securities, gross unrealized gains	840	9
Available-for-sale securities, gross unrealized losses	640	2,455
Available-for-sale securities, estimated fair value	754,220	663,454
Marketable securities, continuous unrealized loss position:
Available-for-sale securities, in loss position for less than 12 months, estimated fair value	352,151	629,033
Available-for-sale securities, continuous unrealized loss position, less than 12 months, accumulated loss	536	2,386
Available-for-sale securities, in loss position for 12 months or greater, estimated fair value	60,325	31,491
Available-for-sale securities, continuous unrealized loss position, 12 months or greater, accumulated loss	104	69
Available-for-sale securities, in loss position, estimated fair value	412,476	660,524
Available-for-sale securities, continuous unrealized loss position, accumulated loss	640	2,455
Time deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	40,000	40,000
Available-for-sale securities, gross unrealized gains	0	0
Available-for-sale securities, gross unrealized losses	0	0
Available-for-sale securities, estimated fair value	$ 40,000	$ 40,000