3. Cash, Cash Equivalents, and Marketable Securities (Details) - Marketable Securities $ in Thousands	Mar. 31, 2019 USD ($) Investments	Dec. 31, 2018 USD ($) Investments
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 1,105,073	$ 1,145,839
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	289	521
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,550	2,656
Marketable securities	$ 1,103,812	$ 1,143,704
Debt securities, Available-for-sale, Continuous Unrealized Loss Position [Abstract]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | Investments	15	15
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 168,020	$ 166,198
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 months, Accumulated Loss	669	834
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	183,310	207,152
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	881	1,822
Debt Securities, Available-for-sale, Unrealized Loss Position	351,330	373,350
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	1,550	2,656
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year	817,992
Debt securities, Available-for-sale, Debt Maturities, Rolling Year One Through Two	196,142
Debt securities, Available-for-sale, Debt Maturities, Rolling Year Two Through Three	89,678
Foreign debt [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	346,931	320,056
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	213	468
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,194	1,878
Marketable securities	345,950	318,646
Debt securities, Available-for-sale, Continuous Unrealized Loss Position [Abstract]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	136,198	150,842
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 months, Accumulated Loss	482	802
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	130,807	94,446
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	712	1,076
Debt Securities, Available-for-sale, Unrealized Loss Position	267,005	245,288
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	1,194	1,878
Foreign government obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	60,385	99,189
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	261	568
Marketable securities	60,124	98,621
Debt securities, Available-for-sale, Continuous Unrealized Loss Position [Abstract]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	21,804	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 months, Accumulated Loss	177	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	38,320	98,621
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	84	568
Debt Securities, Available-for-sale, Unrealized Loss Position	60,124	98,621
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	261	568
U.S debt [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	59,641	44,625
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	76	53
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	95	210
Marketable securities	59,622	44,468
Debt securities, Available-for-sale, Continuous Unrealized Loss Position [Abstract]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	10,018	15,356
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 months, Accumulated Loss	10	32
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	14,183	14,085
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	85	178
Debt Securities, Available-for-sale, Unrealized Loss Position	24,201	29,441
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	95	210
Time deposits [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	638,116	681,969
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Marketable securities	$ 638,116	$ 681,969