5. Cash, Cash Equivalents, and Marketable Securities (Details) - Available For Sale - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	$ 748,916	$ 705,900
Available-for-sale securities, gross unrealized gains	2,128	9
Available-for-sale securities, gross unrealized losses	265	2,455
Available-for-sale securities, estimated fair value	750,779	703,454
Available-for-sale securities, accumulated unrealized gain (loss)	1,900	(2,400)
Marketable securities, continuous unrealized loss position:
Available-for-sale securities, in loss position for less than 12 months, estimated fair value	175,111	629,033
Available-for-sale securities, continuous unrealized loss position, less than 12 months, accumulated loss	234	2,386
Available-for-sale securities, in loss position for 12 months or greater, estimated fair value	45,131	31,491
Available-for-sale securities, continuous unrealized loss position, 12 months or greater, accumulated loss	31	69
Available-for-sale securities, in loss position, estimated fair value	220,242	660,524
Available-for-sale securities, continuous unrealized loss position, accumulated loss	265	2,455
One year or less [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	280,542	290,377
Available-for-sale securities, gross unrealized gains	62	9
Available-for-sale securities, gross unrealized losses	124	406
Available-for-sale securities, estimated fair value	280,480	289,980
One year to two years [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	239,539	228,492
Available-for-sale securities, gross unrealized gains	525	0
Available-for-sale securities, gross unrealized losses	82	1,183
Available-for-sale securities, estimated fair value	239,982	227,309
Two years to three years [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	228,835	187,031
Available-for-sale securities, gross unrealized gains	1,541	0
Available-for-sale securities, gross unrealized losses	59	866
Available-for-sale securities, estimated fair value	230,317	186,165
Foreign debt [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	708,916	665,900
Available-for-sale securities, gross unrealized gains	2,128	9
Available-for-sale securities, gross unrealized losses	265	2,455
Available-for-sale securities, estimated fair value	710,779	663,454
Marketable securities, continuous unrealized loss position:
Available-for-sale securities, in loss position for less than 12 months, estimated fair value	175,111	629,033
Available-for-sale securities, continuous unrealized loss position, less than 12 months, accumulated loss	234	2,386
Available-for-sale securities, in loss position for 12 months or greater, estimated fair value	45,131	31,491
Available-for-sale securities, continuous unrealized loss position, 12 months or greater, accumulated loss	31	69
Available-for-sale securities, in loss position, estimated fair value	220,242	660,524
Available-for-sale securities, continuous unrealized loss position, accumulated loss	265	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