Note 11. Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Assets:
Available-for-sale securities, estimated fair value	$ 509,032us-gaap_AvailableForSaleSecurities	$ 439,102us-gaap_AvailableForSaleSecurities
Foreign government obligations [Member]
Assets:
Available-for-sale securities, estimated fair value	0	25,115
Time deposits
Assets:
Available-for-sale securities, estimated fair value	40,000	0
U.S. government obligations
Assets:
Available-for-sale securities, estimated fair value	3,501	3,502
Fair Value, Measurements, Recurring [Member]
Assets:
Restricted investments (excluding restricted cash)	357,235	279,274
Derivative assets	9,791	8,278
Total assets	877,660	729,543
Liabilities:
Derivative liabilities	16,698	16,204
Fair Value, Measurements, Recurring [Member] \| Foreign debt
Assets:
Available-for-sale securities, estimated fair value	462,731	364,046
Fair Value, Measurements, Recurring [Member] \| Foreign government obligations [Member]
Assets:
Available-for-sale securities, estimated fair value		25,115
Fair Value, Measurements, Recurring [Member] \| Time deposits
Assets:
Available-for-sale securities, estimated fair value	40,000
Fair Value, Measurements, Recurring [Member] \| U.S. debt
Assets:
Available-for-sale securities, estimated fair value	2,800	46,439
Fair Value, Measurements, Recurring [Member] \| U.S. government obligations
Assets:
Available-for-sale securities, estimated fair value	3,501	3,502
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Assets:
Restricted investments (excluding restricted cash)	0	0
Derivative assets	0	0
Total assets	41,602	2,889
Liabilities:
Derivative liabilities	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Foreign debt
Assets:
Available-for-sale securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Foreign government obligations [Member]
Assets:
Available-for-sale securities, estimated fair value		0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Time deposits
Assets:
Available-for-sale securities, estimated fair value	40,000
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| U.S. debt
Assets:
Available-for-sale securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| U.S. government obligations
Assets:
Available-for-sale securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Assets:
Restricted investments (excluding restricted cash)	357,235	279,274
Derivative assets	9,791	8,278
Total assets	836,058	726,654
Liabilities:
Derivative liabilities	16,698	16,204
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Foreign debt
Assets:
Available-for-sale securities, estimated fair value	462,731	364,046
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Foreign government obligations [Member]
Assets:
Available-for-sale securities, estimated fair value		25,115
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Time deposits
Assets:
Available-for-sale securities, estimated fair value	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| U.S. debt
Assets:
Available-for-sale securities, estimated fair value	2,800	46,439
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| U.S. government obligations
Assets:
Available-for-sale securities, estimated fair value	3,501	3,502
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Assets:
Restricted investments (excluding restricted cash)	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
Assets:
Available-for-sale securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Foreign government obligations [Member]
Assets:
Available-for-sale securities, estimated fair value		0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Time deposits
Assets:
Available-for-sale securities, estimated fair value	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| U.S. debt
Assets:
Available-for-sale securities, estimated fair value	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| U.S. government obligations
Assets:
Available-for-sale securities, estimated fair value	0	0
Money market funds \| Fair Value, Measurements, Recurring [Member]
Assets:
Money market funds	1,602	2,889
Money market funds \| Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Assets:
Money market funds	1,602	2,889
Money market funds \| Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Assets:
Money market funds	0	0
Money market funds \| Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Assets:
Money market funds	$ 0	$ 0

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This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a recurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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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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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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The aggregate value of all restricted investments.

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