8. Fair Value Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets:
Marketable securities	$ 1,103,812	$ 1,143,704
Restricted Investments	219,108	179,000
Foreign debt [Member]
Assets:
Marketable securities	345,950	318,646
Foreign government obligations [Member]
Assets:
Marketable securities	60,124	98,621
U.S debt [Member]
Assets:
Marketable securities	59,622	44,468
Time deposits [Member]
Assets:
Marketable securities	638,116	681,969
Fair Value, Measurements, Recurring [Member]
Assets:
Restricted Investments	219,108	179,000
Derivative assets	1,313	2,364
Total assets	1,525,213	1,525,856
Liabilities:
Derivative liabilities	16,362	16,499
Fair Value, Measurements, Recurring [Member] \| Foreign debt [Member]
Assets:
Marketable securities	345,950	318,646
Fair Value, Measurements, Recurring [Member] \| Foreign government obligations [Member]
Assets:
Marketable securities	60,124	98,621
Fair Value, Measurements, Recurring [Member] \| U.S debt [Member]
Assets:
Marketable securities	59,622	44,468
Fair Value, Measurements, Recurring [Member] \| Time deposits [Member]
Assets:
Marketable securities	638,116	681,969
Fair Value, Measurements, Recurring [Member] \| Money Market Funds [Member]
Assets:
Cash equivalents	200,980	200,788
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Assets:
Restricted Investments	0	0
Derivative assets	0	0
Total assets	839,096	882,757
Liabilities:
Derivative liabilities	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Foreign debt [Member]
Assets:
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Foreign government obligations [Member]
Assets:
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| U.S debt [Member]
Assets:
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Time deposits [Member]
Assets:
Marketable securities	638,116	681,969
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Money Market Funds [Member]
Assets:
Cash equivalents	200,980	200,788
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Assets:
Restricted Investments	219,108	179,000
Derivative assets	1,313	2,364
Total assets	686,117	643,099
Liabilities:
Derivative liabilities	16,362	16,499
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Foreign debt [Member]
Assets:
Marketable securities	345,950	318,646
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Foreign government obligations [Member]
Assets:
Marketable securities	60,124	98,621
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| U.S debt [Member]
Assets:
Marketable securities	59,622	44,468
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Time deposits [Member]
Assets:
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Money Market Funds [Member]
Assets:
Cash equivalents	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Assets:
Restricted Investments	0	0
Derivative assets	0	0
Total assets	0	0
Liabilities:
Derivative liabilities	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Foreign debt [Member]
Assets:
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Foreign government obligations [Member]
Assets:
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| U.S debt [Member]
Assets:
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Time deposits [Member]
Assets:
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Money Market Funds [Member]
Assets:
Cash equivalents	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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